Annoying vibration and grinding.

When ever im doing about 40-50mph and up, and i let off the gas a little the car vibrates like crazy. It stops doing it if i let off the pedal all the way or if i give it about 1/3 throttle. It feels like its coming from the rear. What should i look at?

Now for the grinding. When ever im in 1st or 2nd gear and I push the clutch in it grinds, doesnt do it all the time, just more often than id like it to. And also everytime I put it in 5th gear It grinds the whole time, gets worse the more gas i give it, and the faster i go.
 
What tranny are you using? You have serious transmission problems. If you keep driving it, it's gonna ground you soon. Got AAA? It sounds like your case itself may even be compromised, but at the least you have major internal problems. Whichever T you have, you have too much engine in front of it.
 
OK, clarrify some of this for me
When ever im in 1st or 2nd gear and I push the clutch in it grinds...everytime I put it in 5th gear It grinds the whole time
So are you saying that actually pushing in the clutch while in 1st or 2nd makes a grinding noise, or shifting into one of those gear it grinds while shifting? Or is it like what it sounds like your saying about 5th- it constantly grinds while in gear? Does it do it regardless of how fast you are going in 5th, or is it a highway speed only issue? I think there are several things wrong, and all of them are in the tranny. However, driving while these symptoms are happening WILL cause damage to other components, if they haven't already. Don't keep driving it! Thankfully, T5's are cheap and at the very least you should be able to find another one for a couple hundred bucks to buy you some time; and it's relatively easy to swap it in. Good luck
 
just when i push in the clutch in 1st or 2nd, sometimes it happens in 3rd. I thought it was the clutch because it didnt make any noises when i shifted, just when i pushed in the clutch, and it usually only does it if im slowing down. And in 5th gear it grinds all the time, no matter what speed im at.