Squeaks upon startup
 

So I've been noticing recently that sometimes when I crank up the disco it squeaks loudly for a few seconds and stops. Sometimes it does it sometimes it doesn't. The tach doesn't work when it squeaks too. Also, I noticed that im hearing the same sound at roughly 2,000 rmps while driving.
Any ideas why it makes this noise?

Belt or Alternator.
Take the belt off and spin the alternator pulley to check it. How old is the belt? Could be a stuck or hard tunring alternator pulley or a slipping belt.

If your new alternator was a reman unit from a parts store, hope you got the lifetime warranty. The big box rebuild places have a high failure rate, local shop rebuild is a better deal performance wise.

The belt is stopping, hence the squeal and the no tach. But it can also be something else locking up the belt, so check every pulley. You can also put a long stick against the pulley or alternator, and "listen" to the other end with your ear, you'll hear all the hell-raising bearings inside.

Just slipped off the belt and everything seems to spin smoothly...The belt is relatively new, but i noticed that there is little bits of rubber built up on the inside of the the plastic cover and on the alternator as well. Could it mean that it is slipping? Since it mainly does it at startup, wouldn't it be slipping when the alternator is under load?

Sounds like you have a belt wearing, possibly from mis-alignment.

Should I start by putting a new belt on since this one is worn? How could the alternator be out of line?

Before taking it apart, just look down the length of the belt between the different pullies, if one is out to far you will see it. It could be any of the pullies causing that noise.

Make sure the belt is routed correctly, mine was wrong for months after I bought my truck it was working but was not quite as tight as it should have been. When cold weather hit it started slipping and the tach not working til the truck warmed up.

Havent been able to look at her tonight; had a cross country meet...ill check as soon as I get the time to.

Well, Turns out the belt routing was wrong! Not my falt but by a local mechanic who I had the rover worked on after I bought it....That goodness I caught that one! Thanks for the help!