[Al Skierkiewicz]

Phil,
This is a strange one, that is for sure. It is possible you have a bad ground connection in the house. At the entry point, (usually the power meter or the electrical breaker panel) the neutral must be tied to a good earth ground. Usually this is a green wire tied to water pipe. (It depends on local electrical codes.) Sometimes this wire goes inside the panel and sometimes it just connects to one of the conduits near the panel. Check that all connections outside the box are tight and not corroded. DO not enter the box. This is the realm of a professional. If you still can't find a cure, it might be time to call the power company. You said in an earlier post that line operated AM radios had hum (off station) but battery operated radios inside the house did not. If this is the case, it just adds one more piece that doesn't fit.
I still would like to see what the effects are at a friends house or at school. It sure seems like there is a lot of noise riding on power wiring or ground connections at your house.