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Old 06-19-2019, 02:20 PM   #1
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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?

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Old 06-19-2019, 03:01 PM   #2
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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.
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Old 06-19-2019, 04:17 PM   #3
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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.
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Old 06-19-2019, 08:52 PM   #4
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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.
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Old 06-19-2019, 11:22 PM   #5
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Quote:
Originally Posted by Qckslvr View Post
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 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.

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