[kennyt]

Does this receiver have a tape record out?

Many do, and they are designed to allow you to record stereo or whatever and send it back to the receiver to be listened to, if you have that selected, and none connected, you will only hear miniscule sound from the speakers as no true signal is going to the pre/pro, only what is picked up errantly.

I suspect you have something like this that you or someone else accidently hit after the initial listen.... You just need to find it!