[CJFusco]

The more I listened to it, the more the sound seemed like an exhaust leak or something having to do with exhaust... plus I could swear I heard air puffing out somewhere...

...well I was right about the air. After I got the car up on jacks, I noticed that there seemed to be air puffing out from the back of the motor. Sure enough, a spark plug and wire had come completely loose, and both were just hanging behind the engine. Since three of the plugs are well behind the engine, I did not see this the first time I checked things out.

Screwed in the plug, popped the cap on, and we are good as new.

Thanks again for your imput guys, but the solution turned out to be surprisingly simple...