When you hear the noise does it cause a vibration? if you used the wrong half shaft it could be causing the axle to bind. if it is this you can jack the car up and spin the left tire if it jumps up and down then that is it. it could also be in the tranny. my diff blew up once. went to the track and made about ten runs. went home and nothing was wrong about a week later i heard a noise in the diff. thought it was the axle because CRX's with a b16 swap loose the boot off of the right axle often so i thought it was not greased up. i left my house went to my dads house 15 minute ride with no problem. comming home no problem untill i got out. there was a trail of fluid from his house to mine. the center shaft in the spider gears had sheared the pressure pin and slowly worked its way out untill it nocked a hole in my trans. that was a bad night. The noise that it made was a clicking noise, when i let off, but not loud enough to worry about. i guess it is worth checking so jack it up in neutral and spin the tires and listen for the noise in the diff if you dont hear any thing then it is not that.