Noise when car re-starts (using auto-off)

[T350 Brad]

Wondering if anyone can help. When using engine auto on-off (Cayman 981), when the car re-starts, after the engne fires up there's a strange 'clunk' noise, very difficult to describe (perhaps more of a 'thwap', than clunk) - very hard to pin-point but it sounds to me like it's coming from near the front of the dash / wipers area ... Anyone else experienced this or know what it might be!?

I'm not overly concerned, just curious!

Thanks
Bradders

[Ozzie Osmond]

Manual or PDK?

[T350 Brad]

PDK. It does sound like something 'engaging'...? Similar sound to it dropping down into 1st when you're crawling to a standstill.

Edited by T350 Brad on Monday 16th November 11:42

[T350 Brad]

... actaully, listening last night it doesn't sound 'mechanical' (not gearbox / engine) - it doesn't make the noise when I start the car first thing, only when it re-starts!? Has anybody else noticed this?

[bcr5784]

T350 Brad said:

... actaully, listening last night it doesn't sound 'mechanical' (not gearbox / engine) - it doesn't make the noise when I start the car first thing, only when it re-starts!? Has anybody else noticed this?

I haven't noticed it on my 981(PDK) - in fact although I find the auto off very irritating I have to acknowledge that the restart is very quick and unobtrusive. So you may have an issue. It's a pity you can't disable auto off without disabling coast (which seems very effective on motorways).

[ORD]

Sure it's not you coming off the brake and the clutch engaging? PDK has all sorts of weird transmission noises in my experience. It really got on my nerves.

[T350 Brad]

I don't think so, as when I come off the brake the engine fires up, and then as soon as the starting-up noise subsides you get this one slight 'clonk'. Couldn't be anything to do with the auto-wipers could it, sounds like it's coming from that sort of area..!?

[Ozzie Osmond]

ORD said:

PDK has all sorts of weird transmission noises in my experience. It really got on my nerves.

Yes, I suspected the OPs car was a PDK. My limited driving of PDK cars has been accompanied by occasional thunks and clunks in stop/start traffic.

I doubt there's anything wrong with OP's transmission but if the dealer's local I guess it couldn't be wrong to get their input.

[T350 Brad]

THink you're right Ozzie. While on my drive home yesterday I tried putting the car into 'P' when the engine switched off, then engaged 'D' and when the engine fired up there was no sound. Must be something to do with PDK - will enquire next time I'm at the dealers!

[T350 Brad]

So it would seem the noise is linked to the aircon (which I guess would explain why it appeares to be coming from under the dash) ... swithcing it off 'auto' stops the sound from occurring, selecting 'auto' again and it comes back...!

[bcr5784]

T350 Brad said:

So it would seem the noise is linked to the aircon (which I guess would explain why it appeares to be coming from under the dash) ... swithcing it off 'auto' stops the sound from occurring, selecting 'auto' again and it comes back...!

If you look in the handbook you will see that there are lots of conditions when auto stop and restart doesn't happen - all I assume to stop the function flattening your battery too much. I could imagine it might switch off the aircon to ease the restart for the same reason. That said I've not noticed it on mine, and almost always have aircon on. Mine is dual zone - if yours isn't that might explain the difference.

[Ozzie Osmond]

Some cars de-clutch the aircon compressor to reduce the load on the starter motor when starting. Wonder if it's that?

[T350 Brad]

bcr / Ozzie - thanks for your input. It is the dual zone air con - I'm not technically minded but it certainly sounds like the sort of thing you're describing Ozzie, as I could also recreate the noise some times by turning the aircon off and back on!

[bcr5784]

Ozzie Osmond said:

Some cars de-clutch the aircon compressor to reduce the load on the starter motor when starting. Wonder if it's that?

Like I say sounds highly plausible - but I haven't noticed it on mine - and I am a noise freak. So there is some difference.