Is this noise coming from my tranny?

When driving at highway speeds, I can hear a constant whine sound. It's not very loud. In 5th gear at about 50mph, I take my foot off the gas and the noise seems to go away at that instant. Foot back on gas, noise returns. This rules out the tires & rear end. So, can the manual trans make a little extra noise when under load?

It doesn't sound like trouble but I couldn't think of what in a manual trans may be affected.

Thanks.

Thanks for your reply. I'll bet you are right.
The gear installer I had used was quite experienced, thankfully.
When I 1st had the gears installed I did have a noticable vibration.
Soon after, I installed the aluminum drive shaft and it ended the vibration.

Yep, I can see the noise being from the rear gears now. It's hard to pinpoint and not too loud. I'm just curious. I wonder if I ever have the fluid changed to some magical brand like Royal Purple and added the friction modifier of course, if it would help. Some people who have used premium tranny fluids have reported a quieter sound.

Thanks, Bill.