i have an 86 5.0 5spd. 91k mi. whenever im in gear, regardless of which gear, the rear end is kinda loud. its a pretty good volume whine, but only when im in gear... when i press the clutch down (and stay in gear) the whine goes away... i seems to be a little more noticeable on the highway especially.. it gets a little louder when i drive faster but its a pretty consistant pitch... it shifts fine through all gears but occasionally, it clunks into gear slightly when starting off in first, or in reverse. its not a violent clunk by any means though.. is possibly low tranny fluid, or cv or u joint? any help would be great cuz its kind of annoying, and i would like to prevent it from annoying my wallet in the long run. thanks

 

a Whine?
You have gears installed recently?

 

no, stock tranny.. this car is stock

 

Hows the fluid in the rear end? I would guess a differential problem. Bearings?

 

well if it's a whiner in the rear then it's most likey OB..*L*
no really check the oil in the rear...could be a few things like an axle bearing..but I'd also say the rear is worn

 

well thats fantastic. whats the amount of mileage you generally get out of these rears?

 

check fluid and could be ring and pinion worn. I'D put some 373's

 

impossible to say without knowing how it was driven in the past.
btw, there are no CV joints on a Stang.
suggest you pull the rear cover and inspect the gears for abnormal wear and check the backlash as it sounds like it may be too much backlash in the gears now. all gears make some noise but it should not be really noticable in the driver's seat.