Thanks for your thoughts guys. I suspect that all of you are right. What started me on the question was that I put a new graphics board in my PC, and it causes a high pitched squeal in my Peavey amp/speakers. I haven't found any way to fix that, so I decided to try the tiny "LCD" speakers that came with my PC, and - - no squeal! So, I thought maybe these "LCD" speakers were some kind of new technology that prevented the squeal, so I thought I might be able to get some decent speakers w/o squeal. Do a search for LCD speakers and you get millions of hits, but no explanation. The "LCD" speakers have a USB cable (I assume as a power supply) and a 1/8" plug that plugs into the same audio out that the Peavey was plugged into, so I now suspect that there's something about the PC power supply involved in the squeal.