Strange buzzing in drive

I seem to have a strange buzzing that ONLY occurs between about 1800-1900RPM while in gear ONLY. When the car is in park or neutral and you rev to these RPM's it will NOT make the sound. When the car is in drive, it will make a buzzing sound in ANY gear with or without torque converter lockup, and will do it during shifts that may pass that rpm point. It does not buzz at any other time at all and nothing seems to be acting up otherwise. Since it only shows up while moving, I have no idea how to diagnose it. It may or may not get louder under heavier throttle in that rpm range, it's difficult to tell as you can only attempt that during torque converter lockup and the wind noise at the point makes it harder to hear. The buzz sounds a bit like a cross between a generic "buzz" and that weird cartoony sound for electricity. It'll do the sound as long as you're accelerating and passing those particular revs.

Any ideas?

Model is 2001 GTP, about 135,800km's. Recent tune up done including Plugs, wires, PCV valve, fuel filter, newer air filter (aftermarket custom intake @ 130,500km's with high flow filter, which could be the cause of the noise, i don't know?). Transmission fluid serviced @ about 120 sum thousand and less than 1 year ago, all oil changes done on time.

As I did some searching for similar problems online I came across someone who had a similar problem with his Nissan Xterra, turns out his was a loose exhaust heat shield (his even did it in drive only as well). I'll check that out when I get a chance, but other than that, any other possibilities?

Is it buzzing or more of a hum? Wheel bearings hum when they are begining to fail. Here's a thread that might be worth reading...

http://www.automotiveforums.com/vbulletin/showthread.php?t=902900&highlight=wheel+bearing

and if it is a bearing, there are how to's in the tips and maintenance section, heres that link...

http://www.automotiveforums.com/vbulletin/forumdisplay.php?f=2142

Most definitely not bearings. It's a buzz, kinda like a cross between a bug's buzz, and that cartoon electricity sound. I'm still thinking heat shield for the exhaust (crossover pipe looks like a likely culprit)...it ONLY does it between 1800-1900RPM, it almost seems like a harmonic resonance that rattles the heat shield, or at least I think. I found I cannot hear it when it's warm outside, only cold (below 17*C or so, as a guess). Perhaps contraction of a shield causes closer contact to a pipe, therefore causing the buzz.

I'm just hoping it's not something transmission related, although there are no other tell-tale signs of transmission damage. It's definately not the engine or supercharger as it won't do it in neutral.

I would normally just try to figure this out myself, but unfortunately since it only happens when in drive it is very difficult to diagnose. Maybe if I could take the car into a shop and lift it while getting the rpm's to that range in drive (seems like an unsafe idea though).

Are you sure it isn't some sort of pinging? Mine seems to make a buzzing noise all winter and it seems to be up near where the windshield meets the dash. I don't know if its pinging or a vibration that ocurrs at a certain RPM and load. It does not seem to do it in the summer, or I can't hear it with the windows down.

It sounds like it's coming from under the hood, although it is a little hard to tell. I can hear it with the windows down...I don't think it's pinging, i'm sure it's a buzz...it has to have something to do with engine noise or exhaust noise I would think, there's absolutely no vibration that I can feel when I hear the noise, anywhere. It'll do it with the TCC locked or unlocked, but only in that particular rev range. I was thinking of shoving some kind of heat resistant material between the heat shield of the crossover pipe, and maybe the heat shields of the other pipes as well, see if that gets rid of it...