Rearend Whine/Odd Handling/Motor Mount??

I cant help but noticing a whine as i accelerate. As i let off the whine will cut out a few times and stop. But as i start to accelerate again it starts right up. And its really loud if im in 5th at like 40 (and other times whne im in a higher gear than neccesary.) friend of mine thinks its the differential or something in the rear axial. It sound like it in the back driver side. help?

and also when i drive my car will randomly start pulling to the left and right a random times, but then sometimes it will handle fine. I have had recient work on the power steering but dad thinks its my tires needing to be rotated or that my front end is going out. My tires have like 5500-6000 miles on them so i doubt that they need to be rotated. Air is the same in all of them.

And motor mounts...im installing a full exhaust. ARH 1-7/8 Headers and catted y and slp LMII. He says $525 for full exhaust installation but when i asked about motor mounts he said it would be an EXTRA $300!!! WTF? Im getting another estimate but how important are motor mounts?
Car has 79,750 miles or so.

motor mounts are very important with headers trust me.

our rears whine as is..i wouldnt worry about it too much unless it is really really loud...if so sorry bud. time to get a new rear...one that isnt a 7.5 10 bolt.

i would get a alignment done if i were you..also it is a good chance that your tie rods may need replacing

well. the whine is loud enough to keep up with the sound of regular curising speed stock exhuast. so will i need to get a new rear end?

and how much are tie rods? and install?