A Salutary Tale Of Chasing A Rattle

[Geoff Brown]

My R400D is now coming round to its fifth year from build so one would expect that the chassis & running gear has 'run in' with all the the expected groans, creaks & whirs but the car is surprisingly 'quite'.

The BMW LSD is a bit noisy but nothing to worry about but for the last six months there has been this strange death rattle from somewhere on the LHS which appears to be harmonic induced - certain speeds, certain gears etc. Getting paranoid about it.

I have had the car up on sticks & looked every where, nothing. Even thought that it might be caused by the slight panting of the NS skin adjacent to the cockpit, no.

Out yesterday for a drive & there was the harmonic again, like a rattle but not quite......my hands were getting cold so I reached over to the passenger squab to pick up my gloves & the noise stopped! Released hand pressure & it returned. Pressed squab again & it stopped. 

At home on the drive removed passenger seat squab & inspected closely the seat support frame. Adjustment handle appeared to be gently caressing the longitudinal floor bar as evident by the witness mark. Handle 'adjusted' slightly upward using a wooden block.

Test drive proved that this was not the problem.

Further inspected seat frame & check tightened all the small allen drive bolts. Just one at the LH fwd corner was not 'tight' ie up till it shears then back half a turn.

Test drive proved that the one bolt was the issue. A microscopic amount of slackness was causing the harmonic rattle!

So the answer is never discount the small 'unimportant' things while slowly becoming paranoid over a noise. Once again another lesson to store away concerning Sevens.

 

[prangerman]

I had a similar issue for a few years with a buzzy rattling noise somewhere on the nearside which I thought was something in or around the roll cage, or possibly an old rivet in the chassis.

Cleaning the muck of the exhaust earlier this year, I found that one of the clips holding the heat shield on the cat had corroded and was no longer holding the heat shield in place. I replaced both clips and no more buzzy rattling. So simple. I'm glad I didn't embark on removing the roll cage etc...

Peter

[The_ASH]

I've had a similar annoying rattle getting worse for the last 2 or more years on my 2012 metric K engined car. I had tried and tried many times to trace the noise which only occurred at about 1800 to 2400rpm and seemed to be coming from the area under the dash, obviously it never did it when I had another person to hand and mysteriously went away when I went hunting under the bonnet for it. This summer it irritated me to such an extent on one blat that on returning home I decided to continue looking until I'd found it no matter what... transpired it was the bonnet tapping/chaffing on the plastic intake plenum, a search on Blatchat confirmed I'm not alone and that there are indeed 2 different driver side engine mounts for a K series one slightly lower than the other, seems on a Metric car the mount intended for cars with the ally plenum is req'd... only took 2 1/2years to find out! Car now largely silenced apart from the correct noises :-)

[Ray Pearce]

I had an awful knocking noise from the near side. It normally appeared at low speeds, on uneven roads or when cornering. I was pretty much convinced that I needed to replace the rear suspension bushes but couldn't detect any play despite pushing and pulling everywhere. This went on for a month or more before I managed to create the noise with a violent sideways shove on the roll bar. After a few more shakes I finally tracked the noise down. When I ordered the kit 20 years ago, I didn't specify 4 point harnesses, so it came with 3 point lap and diagonals. When I later installed harnesses I left the 3 pointers in place and the noise was the tongue of the belt swinging and knocking against the side skin behind the passenger seat. I still have no idea why it started clonking after 19 years but I was very relieved to find the source.