Oops, sorry. I misread the part about piping through the soundcard.

I suppose that the intermodulation distortion of the particular sound causes the speakers or housing to resonate at their natural frequency. Or maybe I'm just full of hooey, but it sounds good!

Maybe there is software on the PC to do a spectrum analysis of the sound to determine what frequency(ies) cause(s) this audible distortion. Maybe do a frequency sweep on the headphones and see if a fundamental frequency can produce the effect.

Speedy