[MikeMcMo]

My '99 base Boxster makes 3 noises that I'd like to know more about. The car has 54,000 miles and is in great shape and in good tune. I don't think any of these noises are problematic or abnormal, I just wonder if anybody can tell me what they're about.

Noise #1: When I start the car when it's stone cold, for the first half second there's a noticeable clatter from the engine, which goes away right away. Blink and you miss it, but it *is* distinct. Is this metal-on-metal, the pistons hitting the sides of the cylinders, before oil pressure has built up and there is some lube there? Totally normal and unavoidable, right? (Fingers crossed.) This is before and after recent Mobil One oil change.

Noise #2: Upon starting the car cold, I hear an electric motor over my right shoulder, and it runs for the first full minute or 90 seconds, and then you can hear it wind down in a pretty distinct way. Before the car is fully warmed up, that motor will cycle on again once or twice, for just about 5 seconds each time. It sounds cool, I don't mind it, it's another part of the symphony, I just have no idea what it is.

Noise #3: When I'm at a dead stop and I'm letting the clutch out to take off, and not giving it enough gas, if the RPMs fall below about 1,000, over my left shoulder the car gives a pretty significant sigh. It sounds like air being forced out of a bellows. Something to do with the clutch? Any ideas?

The bonus noise is my favorite, that I think even I can guess at. When I pull into the garage (little bit of an echo chamber) and turn off the car, there is a hum that resonates deeply and takes a full 5 seconds before it fades away to nothing. It's my consolation prize for a fun drive coming to an end. I assume it's some part of the exhaust system just settling down for a nap. Well, maybe you know more of the specifics- I realize cars don't really nap. Or maybe they do.

Any light you can shine on these things is appreciated.

Thanks.