Rough idle...maybe?

What is your question?

So I have what I believe is refereed to as a "rough idle" on my 2003 Grand Marquis. While in my car at stop lights it kind of sounds as if one of the cars around me is bumping their base really loud. In fact for a while I thought that's what it was. I guess I would also say it sounds like if you were to lightly roll your tongue with your mouth closed. It doesn't feel like the car is about to stall or anything...it just sounds...weird. The 2 main things I think are worth noting are that when the car is in motion it seems to run fine. Acceleration is great and all that. However at stop signs and traffic light it sounds rough. Which brings me to the 2nd thing I think is worth noting. It only does it when it's in drive or reverse. If I put it in park or neutral it idles fine. Within the last 500 miles I have changed the air filter, cleaned the mass air flow sensor, and changed the fuel filter. This was all kind of a "screw it, let's just do all this other crap while I'm at it" weekend. To be honest I can't nail down exactly when this weird sound started. One reason for that is the blower motor resistor had been broken on my car for several months. So when I was driving it the AC would pretty much always be on full blast. The constant extra noise made it hard to keep an ear out for trouble. This includes ruining a couple rotors. Since I replaced the blower resistor and replaced all the brakes and rotors it's really highlighted the crummy idle :/ Go figure right? Any ideas?