An odd hiss
 

Hello all

Sometime lurker, first-time poster. I acquired a very nice '98 2.5 986 a few months ago on the basis that it was too nice not to buy - very straight bodywork, clean interior, 78k and a service book full of stamps - and have been enjoying it greatly.

Putting it to regular use has exposed a few tired parts that need replacing, the most exciting of which was when the air-oil filter thing let go in a cloud of white smoke. However, it's mostly niggles that need a bit of time and attention.

There is one noise that I can't figure out, so I was wondering if anyone here would recognise the description. On hitting a moderate bump in the tarmac, something towards the back of the car makes a noise that can best be described as a sharp "hiss", a bit like a quick blast of air from a compressor or the sound you'd get from dropping a bag full of 2p pieces onto a table. It seems to happen on the decompression after hitting a bump, if that makes sense, and can be heard whether the roof is up or down. I can't see anything obviously loose in the cabin itself.

Does this sound familiar to anybody?http://986forum.com/forums/uploads02...1560979176.jpg

does this hiss happen right as you hit the bump? How long does it last? Or is it like a quick hiss.

My thought would be a possible blown shock.

It comes from the shock absorber. Check that it is operating as it should. The easiest is to compress it by having you and a friend leaning on a rear fender and then releasing. It should just go up to the original position. If it bounced up and down the shock absorber is shot.

Both of my rear shocks make that noise. They both also seem to be in good working order, so I don't think too much of it.

It is a short, sharp noise rather than something I would characterise as a rattle, yes.

My first thought was a problem with the shocks but I haven't been able to replicate the problem by jostling the car up and down when it's stationary. This may just be because I can't employ enough force, however.

At 78k it makes sense that the shocks might be tired, I guess. The car is on M030 suspension and OEM replacements seem to be £300 ($400?) each, so I think I'll start looking for a comparable aftermarket alternative.

Thanks all.