Weird Squeak

First off I'd like to say hey to everyone... I'm new here... but anywho, I bought a 96 Z28 last week with the 6 speed, it runs great... I cant find anything wrong with how it rides. except a vibration at 90 mph. Okay here it goes... When i let out on the clutch and take off... i can hear this moderate squeaking ... kinda like it squeaks in sevral little chrips... it goes away after a few seconds and then repeats when i hit the next gear up until about gear 4.
I cant tell where it is coming from at all... Also... I put it on the lift today, u joints seem okay... but, there is evidence of a leak from the seal where the driveshaft connects to the rear end. Also there is a TINY amount of play right there.... Thanks for any help!

Hey, update... After driving some more today... It sounds like its coming from the tranny, and also... I'm not entirely sure but when the squeak happens it seems like the stick is sort of hopping or vibrating... Please somebody help me out, I hope was hoping maybe someone had expreienced something like this before and could possible give me an idea of what Im up against here.
Thanks

Okay, I am now POSITIVE it is coming from somewhere around the shifter... hopefully not actually inside the transmission... i took the platic piece over the stick off and i can hear it way stronger.... please someone at least try to help.. worried sick over here.. Thanks again