Inner groove "Rumble"

Might help if you say what turntable, what tonearm, what cartridge.

Marakantz, With much respect, your last statement is a doozy (not a Deusie). Can you say why that would be? Would you say that the converse is true: a new phono stage is less sensitive to rumble? I don't think so. But it does follow from your premise, which should indicate the premise is flawed.

Dear Adam, I haven't a clue. Typical reasons for what you are hearing are that some cartridges can pick up EMI from some turntable motors. Thus, as the cartridge nears the center of the LP, it gets closer and closer to the motor until at some point, hum becomes audible. But this is "hum", not "rumble". Grado and Decca cartridges, IIRC, used to be culprits in this sort of issue (the EMI-induced hum, I mean). Rumble is hard to describe, except I think of it as low-pitched and irregular in frequency. Like Halcro and some others suggested, make sure that there is no mechanical contact being made between arm wand and chassis or platter or other parts of the tonearm, as it sweeps across its arc. Does the cartidge get all the way to the run-out grooves, or does it get hung up? If the latter, then it is some sort of mechanical problem.

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.

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

Adam, Have you checked your turntable bearing? Now that your rumble is generalized, I am guessing you have either run out of lubrication in your bearing and/or your bearing is worn in some other bad way.

Raul, How can you rule out the most obvious (to me) possibility that the platter bearing is worn or low on lubricant? He most lately said that the rumble is audible at all points across an LP. But he has lost interest, and so therefore have I.

Adam, Your dog will probably like it more if you sit with him inside in an air conditioned room and listen to music, rather than taking him on a hike. Just take him out once a day for a romp and a poop. Dogs don't need the exercise