Just toiled down the M1 to get to Bedford and I noticed my car appears to be much more quiet. I have just had new gear cables and an aircon compressor which I am sure have had no effect. However, I always put some duck tape along the side edges of the diffuser where the 6 bolts go through to hold it in place (actually all the bolts except where it gets very hot). I do this to stop the bolts corroding against the alloy diffuser. As the tape was looking tatty I had ripped it off and this time I also put a strip of draft excluder padding, taped in place, where the diffuser meets the body. My hunch is the padding is damping the resonance out of the diffuser tray.
It’s not quiet but I could hear a talk programme on radio 4 at 70mph. There was less thrumming in the car.
Mine seems to have a rattle that kicks in around 4,000 RPM and ends at 4,500. If you are in sixth gear then that translates to 80 mph but it goes at around 85 mph…could that be the same cause?
Good ideas !
I’ll try strips of thin PVC foam tape along all four edges of the undertray.
Not sure how easy it is to find a bead with enough reach around here though.
