996 engine noise recording-what's this then???

[JonA]

Hello,
I have a 996 with 36k miles on it. I've had it since 25k but for the last 5k I've had a slight knocking noise that I've noticed when starting up the engine (don't think it was there before.) This usually lasts for only a few seconds and then goes away. It only happens on cold starts
Yesterday after an unusually long (250 miles) drive the prior day the engine knocking continued for ~30 seconds before stopping. The other difference compared to "normal" was that I started with the car parked on a slight incline with the nose lower that the rear.

Now I know that it's normal for some noise on the 996 engine until the oils works it way to the top of the engine, but this is normally described as a rattling / slightly rough noise, rather than the lower base tone of a knocking. Today I've recorded the start-up noise and would like opinions on this . It appears between ~7-11 seconds in the recording and then goes away. The crunchy noise before I startup is me walking on the gravel of the driveway :-)
The recording is here

Does this sound normal to you guys, do you get this noise, or should I be worried...?
Many thanks in advance
Jon

[lagerlout]

Hydraulic lifters pumping up? Doesn't sound too bad to me but hard to tell from a recording. The 911 engines are rattly buggers at the best of times.

[supersport]

I wonder if this the hydrolic tappets. A friends Evo does this regularly and sounds very similar, sometimes they don't get any oil in them and this is the noise you get.

His often doesn't stop, but will if kill the engine and restarted it.

[JonA]

It always stops....
jon

[ballcock]

Mine does this too .. And I've heard others sound the same.

Is it not the hydraulic lifters / tappets rattling away on start up until the oil reaches them?

It always disappears after 10-20 secs.



Wouldn't trust those rennlist types

[JonA]

Ballcock,
I imagined tappets (+ lifters?) would be a faster and ligher sounding "rattle" rather than knocking. Reassuring to hear your does this too.
I suppose you noticed that I cross-posted to Rennlist.com also then!