Maybe it's your VCR. They made those tapes to clean the heads of the machine every so often.
I've tried them on more than one machine...
Googling told me what was wrong, and even how to fix it (although 1) I'm all thumbs with intricate work, 2) I don't have the time, and 3) I'm not that bothered)
http://www.muppetcentral.com/forum/threads/how-to-fix-sqeaky-vhs.14841/
I'll just watch the ones that still work. So far I forced myself to watch that ep with Joel Grey, and the one with Nog turned Kazon. Another tape wasn't quite so bad, it squeaked occasionally and the picture shimmered every few second, but that was it, the only episode that really suffered on that tape was the one with Chakotay's dad, the rubber people episode..
I didn't bother with The Chute and The Swarm.