I have an '84 944 with an '87 S engine. Everything else stock except suspension. There is a noise I get on startup. Used to only happen after the car had been sitting for a whole day, now it happens pretty much every time I start the car, regardless of temp. Definitely worse the longer it sits. It reminds me of a loose heat shield rattle. It only happens at idle, if I give it some gas it usually goes away, but will come back at idle until the car has run for a minute or two. Didn't make the noise 5000 miles ago when the engine was put in the car, just gradually started making it over time.

I got under the car and checked to make sure everything is tight and not rattling. Banged all over with a rubber mallet to try to replicate the noise (couldn't). It sounds like it's coming from the back of the car. My first thought was something with the trans gears, the torque tube bearings, or maybe the throwout bearing, but pushing the clutch in has no affect on it, so that eliminates anything engine rearward (unless something I can't find is rattling).

If the noise is coming from the engine (which I'll try to verify today by having a friend start it while I'm under it), it doesn't sound like any rod knock I've ever heard. The oil pressure builds less than a second after you start the car. Has anyone had their 944S timing chain make weird noises? I had the valve cover off the other day and it looked fine. The fact that it makes the noise only on startup would seem to indicate an oiling issue to me.

I'll take any guesses anyone has. I'll post a video later if I get the chance.

 

What's the status of your engine mounts?

 

I used the same ones that were on my '84 engine when I swapped, but they're max 2 years old and genuine Porsche.

 

is it possible you have a lifter going flat or the check valve/restrictor in the head is blocked/held open?

if you put a vacuum gauge on the on the manifold it should flutter excessively at idle with a bad lifter

 

Update: managed to get under the car while someone started it today, but it didn't make the sound at all. That was the smoking gun for me. Put it on the ground, and sure enough, it made the noise . My exhaust is contacting my rear sway bar, and banging together at low rpm's. I'll have to make some spacers to hang the exhaust a bit lower. Must have something to do with the swapped exhaust. Dunno why it would have changed over time.