On my Audi A4 Technik I have developed a rattle/ vibrating noise which only happens occasionally. Certain road surfaces I go over you can hear it . It doesn't always happen when I go over bumps
but tends to happen when I come up to road junctions or on certain areas of the road. I have had it in a garage twice and they have done numerous tests but cannot find where it is coming from. Yesterday I went down a steep country lane and braked regularly and could hear it. When I go out my drive over a slightly raised edge I can hear it. I don't hear it going along a flat road and even don't hear it going over sleeping policemen only on certain areas of the road. The only major work I have had done was at an Audi dealer in Glasgow who put all new brake pads and discs on it. The local garage have put clips on the cover under the car and tested all the joints and had it on the machine that spins the wheels etc.
