Mystery bonking noise

[keithvincent]

I know that asking you to diagnose a noise from a text message is like asking for the moon, but I'm at my wits end .... My 1990 Passat CL diesel LHD estate started making a muffled clonking noise from under the floor pan, right side, front, each time it went over a bump in the road or hit a dip. Just sounded as if something was loose enough to bang against the chassis. Neither of my local garages in the UK or France has been able to find the cause. The car has been up on the lift and the suspension etc checked, to no avail. Nothing appears to be loose. Now the noise has become so frequent it is almost regular - every little change in the road surface produces a muffled bonk. It's not allied in any way to the engine revs, and doesn't vary much with road speed. I've just had it re-checked, but still no clue as to what it might be - yet I feel something is in imminent danger of working loose and falling off. To save my remaining shreds of sanity, can anyone offer advice as to what it might be, or where to start looking for the cause? If you do happen to have suffered similarly, and can provide a solution, can you also advise if it's terminal? The car is old, on its second engine and suspension units, but it's comfortable, economical, and an excellent workhorse. There aren't too many of them here in the south of France, so my chances of finding a worthwhile replacement are slim.

[felixthecat1]

Are you sure of the location of the noise. It's strange but sound can move around quite a lot inside a car. You need to get somebody to ride with you and listen out for it. Difficult I know but get them to sit in the foot well and drive around somewhere quiet off the road. Try having them hang out of the window too to see if they can still hear it. You never know it could be something inside the car, under one of the front seats even.

Good luck with it. I know thaose kinds of problems can be madening.

[pontyslapper]

Empty your glove box, cubby holes and your door pockets as well when you test it - I thought my '04 Estate had a problem - turns out the wife had a half bottle of water in the glove box that was hitting the inside of the box and sending the noise through the aircon vent so it sounded like it was coming from under my side of the dash!

[asta]

You will need to try and simulate the noise manually or at slow speeds. Try and bounce the car up and down, rock it from side to side etc. Drive along a bumpy street with your window down.

Is your suspension bouncy, slow or sagging? how does the steering feel?

Have you been back now its got worse? sometimes garages can miss the obvious.

[nealw]

I'm getting a little concerned with where this forum is going. Firstly it's described as 'mystery bonking', then we get a reply from Asta suggesting 'manual stimulation' What next, I await with interest!!!

[felixthecat1]

[ QUOTE ]

I'm getting a little concerned with where this forum is going. Firstly it's described as 'mystery bonking', then we get a reply from Asta suggesting 'manual stimulation' What next, I await with interest!!!

[/ QUOTE ]

You have a dirty mind my friend.

[keithvincent]

Just to tidy up a loose end ..... after following all the advice given (and many thanks to all who contributed) with no success, the knocking (sorry for offending some with the more accurate description 'bonking') noise became much more frequent - and worrying. Eventually my local garage man discovered it was a sticking front suspension leg, something I'd never have thought of. Not dangerous in itself, but a nuisance, and in order to get it through the French Controle Technique, I had to replace the pair. All's well now, thanks - at least with the suspension. See later thread for gearbox problem .....