home theater soud problems

There are many audio-related newsgroups, to which this question would be much better suited. This particular newsgroup is mainly concerned with electronics test equipment, as you can see if you read a few of the postings, which is never a bad idea before posting to a group.

That said: one possibility is that it is caused by a spike on your power line. If your hifi is on the same circuit as something with a motor in it - for instance, a refrigerator or air conditioner - then whenever that motor turns on or off, there will be a short voltage spike.

You may be able to get relief by using a surge arrestor or an isolation transformer; or by shifting the system or the offending appliance to a different electric outlet.