moanin like a wildabeast!

my tranny is talkin to me at around 90, but only in 5th gear. it roars and shakes the car and is drivin me crazy. a buddy said it could be tranny mounts, but i would like you guys input because yall kick ass. please help guys, thanks
 
If it only happens at 90 I would suspect rear end... My rear end has a vibration that starts about 90... at one point I had the gears worn in so there was no noise up to about 100 then it started to creep back down again... so I am thinking gears may be in order within the next year or so...