Me too is sure about it beeing the sub. If I put my ear near the back of the sub I can clearly hear that it is coming from the sub.
I tried moving the sub away to anther room and its still coming from the sub.



Arcam AVR600
Cambridge Audio 640C v2
Oppo DV-980H
PMC GB1i
PMC DB1M-Ci
QS8 v2
EP350 v3