Won't be the bolt's, when they start clicking it's the pin that holds the two halves together.
Can buy them here Alfa Romeo Ersatzteile - Italia Ricambi - Door check, left front door, Alfa 147 5 doors 50512117
a bit cheaper, and they do the door handle plugs that you will also need, although you will need to pay postage on that.
To change them first you need to remove the door card, bit long winded this bit.
4 screws along bottom edge.
1 screw behind cover inside interior door release then carefully lever the surround out and unplug tweeter wiring(unless you have Bose as it doesnt have a tweeter)
1 screw behind plug at top of door pull-this is where you need a new plug for this as the safest way to remove this is to drill a hole in it and screw a self tapper in and pull it out or you will damage the handle getting it out.
1 screw in puddle light at rear bottom of door, and remove cover.
Remove window switch, passenger side just (carefully) prises out, the drivers side has a screw holding it in lower down in the door panel, have a look you will find it.
Finally using a thin flat object(like a trim removal tool) work from the bottom up at the front and back of the card as there are 3 or 4 trim clips each end to release, once this is done you can undo the puddle light from the card, then wriggle it up and it will come out.
Next carefully peel back the membrane covering the door panel, try not to tear it, you only need to remove enough to give you access to the check strap, find the best way in, not sure if I took the speaker out for better access as I was replacing them anyway, then undo the 2 nuts holding it in place, then the 2 that you can see into the body, remove old noisy one and replace with a nice quite one.
Then put it all back together again, and have a beer as you open and close your door in silence