I have exactly the same problem with my system. My EP-500 makes the same pulse noise each time my receiver detects a new surround mode (changing channels on my STB, DVD layer changes, etc.). Just out of interest are you using a Onkyo receiver (mine is a 5 yr old TX-DS696)? I believe Onkyo has a problem with their muting during mode changes and this causes the problem. I had this receiver hooked up to an old Sound Dynamics sub for years and never had this problem which is strange.
Axiom suggested a ground problem from my cable provider may be at fault but I have tried removing my cable connection from the system with no joy. My sub behaves perfectly once I'm thru the menus, etc. on a DVD, until it gets to the layer change.
This is not a cable problem - I've tried several different cables with the same problem each time.
Did you ever get find a solution for this problem?
