Strange noise when driving with low revs

[kramer81]

I have a 98 fiesta 1.3. Whenever I pull away or change up a gear, the 1st couple seconds of acceleration are accompanied with a strange noise (possibly vibration) from underneath the car. If going up a hill in 3rd it will stay for the duration of the hill, as it does with any situation when you are in too high a gear. Doesn't happen when idleing

My guess was the exhaust but the middle and back sections have been replaced and checked by another garage and is apparantly fine.

[Toureman]

If the exhaust is ok it could be an engine or gearbox rubber mounting worn.

[kramer81]

ok thanks, I'll mention next time Im at the garage. Would that not be noticeable when underneath the car? The kwik fit guy did give the engine a good shake to see how secure it was.

[erimus1]

Dounbt it would be the exhaust if it only happens when the car is moving - it is more likely to be something to do with the drive. Could be gearbog or driveshafts?
Goos luck.

[wacky racer]

Does it sound like a rattle, or someone eating crisps. If so the engine is probably "pinking". This is caused sometimes by bad fuel but nore likely an ignition timing problem. It usually occurs when the engine is under heavy load and low revs. Slow speed in 3rd gear or uphill is when you will hear it. This will damage the engine over a low period. You could try one tank of 98 Octane unleaded to see if it goes away. If this cures it have your ignition timing checked.

[kramer81]

Its difficult to describe a noise in words. It sounds cross between a sink draining and metallic vibration. definitely not crisp eating :)

The noise is at its worst if you drive in too high a gear. Strangely it doesn't seem so bad in the morning. I don't know if thats because everything is cold or because there is a higher fuel mix.

It seems to come from directly underneath the cabin rather than the engine bay but I could be wrong.

[kramer81]

PS It is worse with people in the back seats so you could be right, won't do any harm to try some Optimax.

Thanks for all your answers.

It should be noted that this noise has been present for over 3 years and 30000 miles without any obvious effect on performance. In fact, only the perishable things have ever needed replaced.

[kramer81]

PPS The problem started instantaneously after driving hard on a cold morning.