Can't get Guitar Hero or Guitar Hero 2 to work properly on my PS2 Slim

Hi, and thanks in advance. I have a PS2 slim and this question concerns my copies of Guitar Hero and Guitar Hero 2. When I went to play GH2 this evening, the start-up screen loaded at a normal speed but once the game itself began loading, the loading time for every game screen took anywhere between 5 and 10 times it's normal length to load! Moreover, when I did get to finally access songs, they sound completely choppy and are not in sync with the images appearing on screen. I thought maybe it could be the game, so I tried Guitar Hero (the first one) and it pretty much did the same thing, except it loaded to a certain part of the intro, where the video froze and the sound kept skipping like a wayward CD. At this point I thought something was up with my PS2, so I tried a couple other games, and they worked completely fine. No loading lag, no gameplay interference, and all the sounds etc. match up. I'm stumped as to why it's only affecting GH and GH2? I doubt this is a "known" issue but perhaps you can help me figure things out. I really don't know if this is a hardware or software issue anymore, so I took a chance and posted here. Thanks again for your time! RF81