It was the first sub in the chains output.
I need to manually turn off the 1st sub in the chain and don't always remember to when leaving the room. While turning everything off tonight I heard the same sound I was hearing previously from the sub I was concerned about (last one in the chain). As soon as I turned off the first sub (within a second or two)the sound stopped. It appears the 1st sub was outputting a signal when none was being sent. This time my receiver had been off for 4-5 hours.
This should mean my 2 best subs are still functioning properly.

Edited by brwsaw (04/28/14 03:24 AM)
3 M80HP
2 QS8
2 QS4
ADA 1000-4
Seymour XD
7'x 12'x 21' cave
3 Paradigm subs