Brand new M3 - odd noise

Greetings,

Just picked up my new M3 Touring Edition today. I have to say, I absolutely love this car. It's the first stickshift I've driven in 10 years and I'm loving it.

Quick question for you guys. While testing it out today I noticed an odd noise that sounds like it may be normal, but I haven't the foggiest what it is. This might be hard to describe, so bear with me.

I noticed it while moving 90km/h on a straight stretch of road. Every 5 seconds or so I would hear a "pssssht" type noise from the passenger side/rear of the car. The best way I can describe it is like it's expelling air or something. It reminds me of the sound a nitro burst makes in the movies only much quieter and very quick. I wouldn't have noticed had I not turned off the radio to listen to the car. Any ideas?

Fire

Well, I read through the manual and the only thing that seemed close to what I am describing is this. (But it says you will hear it only when the engine is off)

Note: While the engine is off, the sound of a valve opening and closing can be heard at the rear of the right side of the vehicle, however this does not indicate an abnormality. Your vehicle has a self-checking device and it operates while the engine is off.

Sounds fine and dandy, but it doesn't say if it's abnormal to hear it with the engine on, lol! What do you guys think?

Fire

I don't have a "pssssht", but I do have a rattle somewhere on the passenger side that seems to revolve around the sub-woofer. It's not constant, so tracing it is a real bitch.

Sorry, no "pssssht" :)