Strange Squeaking noise underneath......

[boxtops]

I have a nice little Daihatsu Sirion. It has started making an occasional rattling squeaking noise which appears to come from "underneath" but I can't pinpoint it, but it's quite noisy when it happens. It seems to happen more when I am going downhill - and conspicuously starts sometimes after I have been over three speed lumps which I have to traverse on the way back from the supermarket. It sounds to me - a complelte mechanical layperson - like a ball-bearing come loose, but someone else said it could be a loose baffle in the exhaust. I know not, and would appreciate some thoughts from prople who know about cars. I could take it to my garage but if they take it for a test drive, it won't do it - it seems to be the downhill angle that sets it off. What's up, what do you diagnose?

[Answerprancer]

I would bet it's one of those U-shaped brackets that clamps the exhaust system come loose.
Park it with the engine running, gently and slowly increase/decrease the gas and see if it happens when the revs reach a certain pitch.
Have a look, or get someone else to look underneath to see if there is something dangling from the exhaust system.

[Hopkirk]

It could be a heat shield, which protects the car from the exhaust, has moved or been bent.

It might just need pushing away from the exhaust, or refixing in some way.