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Discussion Starter #1
Ten days ago I had a replacement windscreen fitted. Since then I have been very aware of what I can only describe as an induction noise. When I put my foot down on the throttle there is a hollow sucking noise and on lifting off a distinct "cough". I am sure I did not hear such a noise before the windscreen was changed but I cannot see how the two things can be related.

The only other time I have ever heard such a noise was many years ago when a car was run without the air filter fitted. The performance of the Giulietta has not changed, acceleration is the same, mpg achieved on a run up to Edinburgh on Friday was about 43 so no significant change.

This is the first turbo engined car I have had so have nothing to directly compare it with. Is it normally to be able to hear the air being sucked in? Why should changing the windscreen make a difference? The only thing I am not sure about is whether or not the original screen had low noise transmission glass as described by CS155 here http://www.alfaowner.com/Forum/alfa-giulietta/992642-windscreen.html post #15. Could someone with a MY2011 and original screen have a look and see if the "ear" symbol is present.

Any other suggestions for a cause will be very welcome as I tend to worry if I do not understand or know the cause of changes.
 

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Discussion Starter #2
So should I be worried something has broken? Googling seems to indicate that induction noise equates to split hoses but that was in the Mitsubishi and Ford forums.

Can nobody set my mind at rest or tell me to get to a mechanic pronto?
 

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Ten days ago I had a replacement windscreen fitted. Since then I have been very aware of what I can only describe as an induction noise. When I put my foot down on the throttle there is a hollow sucking noise and on lifting off a distinct "cough". I am sure I did not hear such a noise before the windscreen was changed but I cannot see how the two things can be related.

The only other time I have ever heard such a noise was many years ago when a car was run without the air filter fitted. The performance of the Giulietta has not changed, acceleration is the same, mpg achieved on a run up to Edinburgh on Friday was about 43 so no significant change.

This is the first turbo engined car I have had so have nothing to directly compare it with. Is it normally to be able to hear the air being sucked in? Why should changing the windscreen make a difference? The only thing I am not sure about is whether or not the original screen had low noise transmission glass as described by CS155 here http://www.alfaowner.com/Forum/alfa-giulietta/992642-windscreen.html post #15. Could someone with a MY2011 and original screen have a look and see if the "ear" symbol is present.

Any other suggestions for a cause will be very welcome as I tend to worry if I do not understand or know the cause of changes.
I think the low noise transmissian glass is standard. So far all I've seen have it, but I've never seen a RHD...
 

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So should I be worried something has broken? Googling seems to indicate that induction noise equates to split hoses but that was in the Mitsubishi and Ford forums.

Can nobody set my mind at rest or tell me to get to a mechanic pronto?
I think there's a chance the glue isn't uniform around the glass, maybe there's a hole somewhere. If you have the possibility, have someone blow compressed air aound the edges (particulary the bottom, so remove the wipers and the plastic cover) and listen if you can hear it change note. You'll know when it happens.

The induction noise is there, but you shouldn't be able to hear it from te inside...
 

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Discussion Starter #5
Thanks for that. I have double checked the markings on the new screen and can see the "ear" symbol which I had missed before so obviously not a sound transmission problem.

I will try and get my friendly mechanic who does all the work on my other car to apply his airline and we will see what is what.

If there is a hole can it be sealed without removing the screen?

If so I think it is worth approaching National Windscreens who fitted the replacement but given it is likely to crack on removal I cannot imagine they will be prepared to refit another replacement. Anyway so long as I know the cause it is possible to live with it provided, of course, the screen doesn't leak.
 

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Thanks for that. I have double checked the markings on the new screen and can see the "ear" symbol which I had missed before so obviously not a sound transmission problem.

I will try and get my friendly mechanic who does all the work on my other car to apply his airline and we will see what is what.

If there is a hole can it be sealed without removing the screen?

If so I think it is worth approaching National Windscreens who fitted the replacement but given it is likely to crack on removal I cannot imagine they will be prepared to refit another replacement. Anyway so long as I know the cause it is possible to live with it provided, of course, the screen doesn't leak.
If they fitted it incorrectly they should fix it for you foc - Autoglass do.
 

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A basic rule of diagnostics: the first thing you suspect is the last thing you changed. I'd suggest that either the new windscreen hasn't been fitted properly or, despite having the "acoustic" logo it doesn't meet OE standards.
 

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I think that it may be worthwhile checking that the plastic scuttle panel below the wipers has been refitted properly: there are a few rubber bungs/gaskets that are supposed to isolate the interior from exterior noise there. I know when my sons C1s windscreen was replaced the repairer said that the windscreen had been replaced previously because the locating pins used in the factory were missing - and these left holes in the bodywork around the windscreen. He filled them with mastic....as you do!
 

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Discussion Starter #9
An appointment has been made for Monday with the depot manager.

I am becoming more convinced it is a problem with the fitting. Thinking back, the fitter had a problem getting the plastic scuttle panel to bed back down against the glass and told me he had eventually resorted to putting a block between the fascia and the glass to get something to push against as the glass kept flexing. If so then surely the mastic may well have been insufficient to provide an adequate bond.

I will keep you posted.
 

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Hi Tony, I have a RHD and cannot find the "ear" symbol. Where should it be? bottom right? near the Alfa logo?
 

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Discussion Starter #11
Driver's side below or the manufacturer's name and codes. Just above the black stipple band
 

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Discussion Starter #14
Update as promised.

National Windscreens will order another replacement windscreen and refit it. No arguments; the manager listened to what I said, checked that the present replacement was acoustic, and said he would order the replacement by St Gobain rather than AGC (the present screen). He explained that occasionally air bubbles can occur in the mastic which when it dries out can leave a hole or that the mastic gets "rolled". Either way, apparently, it does not need much of a hole for noise to be transmitted. This time the manager will fit the replacement and have another fitter on hand to help lift it into place. He is clearly not taking any risks of getting it wrong a second time.

The frustrating thing is that,while the original chip was not very big and even with the radiating cracks was within the 40mm diameter for a repair, two of the four radiating cracks did not take the resin and hence it needed the new windscreen. Had the cracks been that little bit wider then they would have repaired and all this hastle would have been avoided.
 

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Discussion Starter #16
That was what I thought but all the other glass is St Gobain so I think he assumed that AR would have used the same supplier throughout
 

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no, the screen is AGC, and the privacy tints in the rear doors are AGC aswell. the front doors have saint-gobain, not sure what teh window in the hatch is and it's raining now so not going out to check ;)
 

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Discussion Starter #18
My rear windows and hatch are all St Gobain. I couldn't swear to it but recall looking at the original after it was removed and seeing that it was the same as the replacement ie AGC. Tomorrow is crunch time and we will see what is fitted. So long as it is fitted properly and is quiet I am not really bothered who made it.
 

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Discussion Starter #19
Final Update:

@ CS155 In the end they fitted another AGC screen.

With the new (2nd time) screen the noise levels are back to what I think I remember with the original screen.

When the manager delivered the keys to home so that I could collect it late afternoon to allow the mastic plenty of time to cure he told me the following.
Before starting he took it round the block and could immediately hear the problem.
He then taped up the scuttle and repeated the trip round the block. The noise had gone so definitely a window problem.
On removing the original replacement he found that, in positioning the glass, the mastic had been rolled up low down on the drivers side. This meant the mastic had not bonded to the glass and the resultant gap was sufficient to transmit the noise.​

Low down on the driver's side was exactly where the technician had had problems seating the scuttle and resorted to a block between screen and dash. Clearly the misplaced mastic was not supporting the screen and hence permitting the flex in the glass that he could not overcome when pushing on the scuttle. I don't know if, had he realised what was wrong, he could have removed the screen, without damage, before the mastic had set and started again. Anyway it is too late for that and it has cost them another screen.

Currently I can still hear some induction noise when I lift off the throttle but I think this is down to having been made more aware of it with the increased sound level with the faulty fitting and it was probably always possible to hear some engine noise. Coming from a Xsara I found the Giulietta much quieter and so was probably not registering exactly what level of noise there was from the engine as opposed to the tyres and exhaust.

Many thanks to all those who provided advice and to any one else in a similar position I would say do speak to the windscreen company as I got the impression that this is an occupational hazard and not a problem they are unaware of.
 
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