I would record the noise but it is gone now..I am almost positive it's fuel pump related. I had gone down to "E" like 30 miles left to go on the on-board comp range function and put 10 bucs in at a shell gas station that i had never gone to before. On my way to work after that, the noise started. After work i filled up w/ 93 mobil and let the car sit. 24 hours later the sound is gone. The noise was a really loud hum/buzz. So im gonna chalk this one up as problem solved, but monitor of course and take alpine's advice of replacing the unit all together as precautionary main..