Hi jmone (Nathan),
I just chatted with Tom Cumberland, Axiom's chief engineer who designed the amp and electronics for the EP500. We have never heard of this problem before, but we do have thoughts on the source. Here's how to trouble-shoot the problem, which may be related to the HTPC (presumably, it's interconnected through your system to the EP500).
First, remove the audio input cable(s) to the EP500, so it is only plugged into the AC wall plug, and has no other cables connected. Does it still burp? If not, then we know the disturbance is somehow coming down the sub audio line from elsewhere in your system.
Now find the hard OFF switch for the HTPC and turn it off. The HTPC would still remain alive in a standby or hibernate mode, and we think it may be a recycling glitch in the PC power supply. These typically have little of no shielding so that noise could be delivered through the interconnected grounds of your system.
Anyway, turn the HTPC hard off (no power), then re-connect the audio input to the EP500. If the sound is related to the HTPC's power supply, it should be gone.
Let us know how it turns out.
Regards,
