T-5 Transmission noise

I have a '95 Gt coupe, the car has a good deal of engine work but retained the stock T-5. Rcently the car has been making a high pitch squeak, that starts when i get on the gas in gear, but does not occur at idle. I changed the differential fluid thinking it might be the diff, which it wasnt. I also WD-40'ed the universial joint and where the trans joins the driveshaft. Neither helped. I added some grease to the universial joint, which also had no effect. The noise sounds like its coming from about 6-8 inches behind the shifter.

Any ideas?

Thanks,
Erik

No it doesnt, it only happens when there is a load going through the trans, with the clutch in or in nuetral it doesnt make the noise,

Erik