Funny, but I went through this just yesterday.
I have a ProJect RPM-1 Carbon and recently replaced the US-spec Sumiko Pearl with an Ortofon 2M Red cartridge. I use a ProJect Phonobox MM amp. After a couple months (very intermittent use) I started getting a serious rumble at higher volume. I mean "talking loud", not blasting at "11." This never happened with the Sumiko, and I had a couple of months of no problems with the new cartridge.
Yesterday I got out all the tools and re-checked tracking force, verified the 3-point "legs" of the TT are on their pads, reset anti-skating, cleaned the stylus, everything possible. I was still getting it. I then switched the receiver from "Stereo" to "Analog Bypass" to take the subwoofer out of the picture. Problem gone. I can go as high as I want now, but my speakers aren't giving me what a subwoofer does.
I'm going to try isolator feet on the sub. I cannot move the TT, there's just no place to put it. In fact, the whole reason I have this TT is because the space I have won't fit a proper TT and this one is tiny. We'll see if isolators on the sub do anything, and I'll try a damping method of some sort under the TT too. I just wonder what's going on with this in that I didn't have a problem for a year & a half, until now.