Inner groove "Rumble"

Looking at your system photos I am struck by the fact that your problem area is directly beneath the power transformer of your amp.Why this would suddenly become an issue I have no idea.But the first thing I would try is to move the turntable two inches to the right (or the amp to the left).I would try this first because it would be so easy to do.I spent four hours last monday ridding my front end of sudden noise infestation,it can be maddening.When it's back to normal Life becomes so good.Good Luck.

A la Casey's good idea, this speaks also to the question of whether you are hearing "rumble" or "hum". The power amp transformer could induce hum, not rumble.

It's definitely not a "hum." The interference is a very irregular "staccato-like" popping type of rumble, which is now starting to bother me even at the outer grooves of a record. I removed and replaced the belt, moved the sub-platter up and down a few times within the bearing, checked the cartridge wire leads, checked the anti-skate, removed - cleaned - re-plugged the phono interconnects, ...... and still the problem continues, now anywhere along an LP's surface. Oy Vey !!

"staccato-like popping" Can you guess in what frequency range? Rumble is very low frequency stuff, as the name suggests.

Yes ...... low frequency.