I was able to reliably send commands to insteon devices from my pc through the PowerLinc with the line noise present. I assume it was doing retries.  However I was not able to use any software that would do auto discover, or link anything to the usb unit.

There is an LED on the PowerLinc that would flash horrifically as soon as I turn my computer on. So I knew the computer was introducing the line noise.

According to SmartHome technical service a noise filter such as the 1626-10 FilterLinc would fix the problem.

I received the the FilterLinc, plugged my power strip into it and it solved the problem.