Hissing sound when engine running - even at idle..
 

I seem to have a "hissing" sound coming (not loud) from the 944 when I drive it, and still when I idle. It is difficult to tell where it is coming from.. sounds like it may be underneath the car.

I have noticed that the car smokes a little more than normal from the exhaust.. I'm pretty sure it's not a broken hose as most of them they have been checked/replaced recently.

Any ideas? Could this be a transmission issue perhaps?

Vacuum leak?

Balance belts normal whine?

Are you having any other symptoms or just the hiss?
If your idle is high (over 950) it is probably the vacuum

AHH, I hate noises like that, I still am trying to find a hissing metalic rattle that only happens on decel, I have been chasing it for 2 years. Good luck. It might be a heat sheild or a exhaust leak

Everything else seems ok.. but when I drive down the road I don't sound a smooth porsche!

It's loud as in you don't hear it in traffic or busy area, but if you drive down a quiet residential street it is quite noticeable.. (oustide the car).

What's the "balance belts normal whine?"

Kinda sounds like a light supercharger wine

Well, it's not a turbo..?