S/C Noise

Ok, to start out I got my gtp about 4 months or so ago and it had no s/c noise (that I knew of...I didn't really know what to listen for). About 2 months ago I put the car in reverse and this sound came, and its really tough to describe but it was high pitched and kind of... scrapy/metal. I accelerated a little and it went away. Then I went on here and heard somebody say something about s/c noise, since then I can pick out a whistling noise when at low enough rpm's that the engine doesn't cover it up(kinda sounds like a car low on power stearing fluid, but not as bad). About 2 weeks ago the noise got worse and eventually went to that sound I mentioned earlier (first one). So I immediatly parked the car and waited until morning to check the oil. Morning came, we checked the oil, and couldn't see it, dipped the hex wrench in and saw that it was pretty low (oil looked very clean). Went out to the dealership and I bought 2 bottles of the s/c oil ((side question, they told me that it would take 8 bottles to fill it ($80!!!!s) is that right?)). It took a little less than 1 bottle to fill it to the bottom threads of the screw. Since then the whistling noise seems to always be there when the engine is warm, when cold it seems to not be there/softer. Last piece of valuble info would be that my car has 124k on it but when I got it I went through the dealer to the seller of it and she replaced the s/c at about 112k or so.
So with alllll of that backround info, I figure there is damage done to the s/c because I was an idiot and didnt check the oil when I got it(even though it shouldnt have needed a change for awhile longer). So finally I was going to see if anybody had some info on:

Any further damage that will likely happen/remedies
What exactly that sound is
Ways to get rid of the sound
Remedies for anything elseThanks for reading all of that if you got to here. Thanks for any info too.
-Kyle

A high pitched whine you describe is probably a bad bearing in the supercharger snout. You can purchase a kit to rebuild these snouts but you will need a press to do it. Or you can find a machine shop to do it for you. Just don't let anyone talk you into scrapping the thing as it can be rebuilt. Also make sure to check the tensioner pulley as they can go bad. This may be the entire issue but you will have to check.

As for 8 bottles of oil, that guy must like the taste because it will only hold two bottles when empty. If you tried to put 8 bottles in you would bathe the entire engine in the stuff and it would fly all over the place.

Unfortunately, the lesson you learned is to never assume and make sure you check everything when you purchase a used car. This one shouldn't be too expensive though and if you have to rebuild it replace the coupler while you are at it. This will save you some hastle later.