Undertray rattling
 

Hi folks. I get rattling from the front end at above 70mph, and it gets worse in heavy winds. I'm pretty sure it's the plastic undertray, as it flexes some when I push on it, and there's some metal parts it is covering with only a few mm of clearance. I can flex the undertray with one finger and have it make contact, so I am guessing that's what is giving me a little rattle.


Anyone else experience this? My undertray has been off and on a few times for header installs, but it looks solidly in place and everything.

There was a thread regarding this with some pics as to which bolts were causing the issue. I used some neoprene (rubber) bolt washers from Home Depot. I can't recall if they were 5/16" or 3/8". There is more info in that thread if you can dig it up. Basically, the North American cars don't get the full plastic shielding on both sides under the car, but the bolts are the same on both sides of the rear undertray, so the ones on the pass side are a bit long. This lets that side of the undertray rattle around a bit.
There is also a thread on the rear inner fender liners causing this sort of sound, that gets worse with speed, or on a windy day. When I first heard this one, I thought it was coming from the front/rocker area, but a closer listen lead me to the liners in the rear wheel well. Same thing fixed the problem...neoprene bolt washers.
If you can find those 2 threads, I think you'll have your problem licked.

Could also be a small stick/stones/or in one persons case the positive battery terminal cover.

Hit a few things with the palm of your hand and see if anything vibrates and rattles. Before the splitter I would always get small gravel in there.