Bill, I had the same problem a while back. And it turned out to be just a DSP setting in the sound card audio manager had somehow got turned on. I think it is probably a software not hardware issue.

Check the DSP panel for your soundcard and see what is turned on.
You should be able to find it in Control Panel. I think it was the Realtek Audio Manager on my PC. Somehow one of the "Environment" presets had become active.