Driving yesterday I started to notice a sound that at first I thought was a hole in a tire. It sounds just like that, but I checked the tires, and the sound only happens while the engine is running. I do have a CEL on emissions control system - small leak, but this leak doesn't sound very small and I don't know if it's related. Probably not too important, but I only hear the sound when there's something on my left side to bounce it back at me. It's not loud enough to hear on its own. I don't have any problems with how the car's running, idle seems a bit more choppy but nothing that would concern someone who isn't as paranoid as I am...

Probably unrelated, about 3-5 miles of driving before I noticed the sound, I did grind my gears going into second... stupid shifter got stiff on me

 

it's probably a vacuum leak somewhere. when the engine is running spray some starting fluid around the vacuum lines slowly and see if the sound stops or the engine changes its idle. that will tell you where the leak is.

 

Thanks. If that's it, is that detrimental or can I live with it for a while?

I also just remembered that it makes the same type of sound, a bit louder though, when I'm accelerating / usually between 2-3k rpms

 

after it starts making that noise again look under the hood, may sound weird but water pumps have a little hole that goes out when they start to go out and somtimes the hole only opens to the size of a pen hole but that will spray a mist of water out, not saying thats whats wrong but its somthing to check, it would relate to it starting after driving it a bit, the water getting pressurized when heated..... but most likly like said above its a vacuum leak.