You ever hear hondas reverse? Its that kind of noise. Not extremely loud, but not dead quiet. I'll be in second, bring it to about 3k rpm, and let off the gas, and let it whined down in second. It makes the whining noise. then if I slowly accelerate in second, above 2.5k rpm, it will make the whine again. I dont think it does it under hard acceleration. The car has been running fine. idk what it would be, hopefully not a transmission problem, though i've read some 370z's do this too, the syncros trying to catch up? needs a trani flush? my transmission going? Not sure.