I don't know when this began, but my car has been pretty quiet, although my car is pretty quiet to begin with. The difference is before, you used to be able to hear the rumble, and now it sounds like air. My initial assumption is the catalytic converter.

Here's what happens:

I rev up a little. The sound comes more near the passenger than the driver's side.

The sound is, well, I should have recorded it, but it's hard to get a real good sound byte...sounds like it's blowing air that is in sync with the RPM. For example, at 2k, it's quieter than if it was at 4k.

I'm just wondering if this should be something to worry about or not.

Mmmm, if your cat is shot, it wont get quiter ussually. In fact you'll notice no real change. I wouldnt worry about it though.

It kind of sounds like a vacuum cleaner in reverse. It's just really annoying and I hope it doesn't lead up to something bigger. I've never experienced this before with my car (I do most of the work).

Maybe that's a sign you should cut your music down a little bit.... :)