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The weird thing is why are my front speaker drivers rumbling too when signals below 80 Hz are being sent to my sub?

Craigert, Re this last post, define "rumbling".  Are you hearing a noise or are you watching the drivers do a dance, in and out?

The weird thing is why are my front speaker drivers rumbling too when signals below 80 Hz are being sent to my sub?

Looking at the manual for the AV7704, I see that depending on some menu settings frequencies below 80 Hz may or may not be sent to the main speakers, in addition to being sent to the sub.

Also, I don't think an answer has been provided to a question I stated earlier, namely "does the problem still occur when the sub is not operating? "

Regards,
-- Al
  

Oops sorry I forgot to check your question Al. When I get home tonight I will play a record without the sub and will report back!

Thanks for reading my manual!

There was only one time there was audible noise that came from one of my front speakers, but it’s pretty much just noiseless extra flapping of the cones and woofer. 

Ok Al I moved the fronts forward of the turntable and it appears only the subwoofer sitting next to the TT is rumbling now.

When I turned the Sub off there was no rumble present.

Is it safe to assume that the rumble in the Sub is feedback?

I am giving my boy a bath right now but I can try to relocate the sub to see if it all disappears. 
One thing is for sure, I need to buy an outboard preamp so I can get rid of that phono cable extender. It’s horrible. I’m surprised so many people have recommended to just extend it. The hum is so bad it’s not even listenable. Rega seemed adamant that it’s a certain length for a reason. I’m a total believer now.