funny noise??

[DoctorBonzo]

recently noticed a slight whiring noise from my 52000mile MGF when accelerating gradually in second gear 2000-3000rpm. Its like the sound you get when you're not in reverse properly. It goes away when accelerating hard and the car performs as well as always. Its not there when I rev 2000-3000 in neutral and I haven't really noticed it in any other gear.
Any thoughts on what this sound might be? Puzzled

[wildoliver]

Is it on and off the throttle? If so sounds like slop in the drive train, if it is a constant chuntering groan on and off the throttle my guess would be final drive (diff) wear.

Hows the gearbox oil level?