Rumble sounding bonk over small road defects.

[Willpower]

What about the wheel well liners ?

[raypaice]

Yes they are on my list too. But they are of a softer material so less likely. I think I am at a stage where I have a lot of expense of replacing bits to sort it so may have to leave it until it gets noisey enough toidentify it.

[Huxie]

Absolutely no help I know, so apologies in advance, but your ongoing efforts to resolve this put me in mind of this old advert. Perhaps you need to think outside the box 

http://youtu.be/JF-KJ5-KNQk

[Willpower]

Yes they are on my list too. But they are of a softer material so less likely.

To use your Wobble Board analogy, I would think being a softer material would actually make it more likely.  No ?  A bit of cardboard can make a wobble board noise.