All weather setting
in heavy use
Join Date: Jun 2007
Location: Near York, UK
Re: Persistent hum on 147 JTDm
Looks like I might have solved this.
The problem is that my nearest Alfa service centre is 25 miles away. On the rare occasions I was passing, the car never obliged by making the noise.
But last night it did. So I stopped by Piccadilly Motors of Knaresborough, kept the engine running, and they diagnosed it as a vibrating fuel supply pipe (situated under the hinged end of the bonnet, quite close to the back of the engine bay). Apparently it is made of rubber-coated plastic which vibrates under certain conditions and makes a loud noise. So they are going to replace it with a rubber pipe. It's a known problem, apparently.
Mystery solved. I hope.