Mike Murphy

I finally pulled the serpentine belt and determined that it's not any of the pulleys. The noise is still there. I guess it sounds like chains to me, so maybe I need new tensioners.

AnthonyGS

There are a lot of engines that have lifter rattle on startup especially if they sit a long time between starts. My 996 does it on cold starts ifbit sits a few days. If I'm driving it for a few days multiple trips and the oil and lifters don't have time to drain and pump down, nonstartup noise. I feel this is one of the disadvantages of a boxer engine compared to a V or inline. Lifters in a V or inline will retain more oil, but their disadvantage would be its likely dirtier oil.

I'm not certain but worn timing chain guides and chain rattle would probably be quite a bit louder and sound more random and less steady than lifters.

If if I ever have to replace the AOS or get to some major maintenance, I feel replacing the chain tensioners would definitely be worthwhile.

twitchett

That is unfortunate. Mine still seems to be correlated with weather when it comes to volume and length of time that it runs noisy. When the weather is hot it starts quietly, but any days that dip into the 40s for temperature and the car makes the rattle/tapping sound. Not quite the same sound as scored cylinders, but scary nonetheless. For example, today was 55F and I had the rattle for 1-3 seconds and nothing right on startup, so I would think it is the chains. Car has had this sound since August of last year and when I took it in for inspection this April the sump and oil was clean as a whistle.

Mike Murphy

Well, upon further review, a lot of folks that have had this issue with noise, and they have replaced one or both tensioners, even IMSB and other items that were replaced such as chain pads, and they still had the noise.

So, I shouldn't have been so quick to say "tensioners" because I'm not sure that's it. Sometimes it sounds like a rod or piston knock, sometimes it sounds like lifters and valves.