I have a Technics SA-690. When I play it at half volume, I soon hear a loud crack and the speaker on the right stereo channel has a subtle but audible, high pitch buzz which varies direcly with changes in volume level. The next day the problem is gone as long as I keep it below 1/2 volume. I swapped speakers and wires. I think the problem is with my receiver. Any suggestions? I don't want to buy a new receiver if I can fix this. Thanks.