Yes, the sub is set to "auto-on", so I hear the boom only when it gets a signal below 120 Hz and turns on from standby mode. I can flip the switch to just "on" and see if that replicates the noise. I'll try your procedure of letting it set overnight and see what we get.
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Update: After reading your comments, I tried the following:
1. Flipped the toggle switch to "on" from "auto"; watched TV as normal and it happened right away - this didn't tell me much.
2. Shut everything down and replaced the cord from the amplifier to the sub; it still happened - problem not the cord.
3. Turned the power back on and let the sub sit; I heard one boom without any input signal - problem is the amp.
Now, where do I get the replacement part?
Thanks for the help. I noticed right away my music lacks depth without the sub. No comparison.