Rumble is different than acoustic feedback. Rumble is noise from the turntable usually related to the bearing and can indicate a lack of sufficient lubrication or an issue with a worn bearing. Acoustic feedback is caused by bass energy being transmitted to the turntable system which results in a roar that builds upon itself getting louder and louder until you lower the volume. Acoustic feedback can be addressed by better isolation for the table like a wall shelf usually provides. What you're describing sounds like rumble, but if it's only on certain records it can be in the recording or on a worn record. The Harbeths may not have reproduced such low frequency info like your larger speakers do which made the rumble audible. Check the platter bearing of your table for proper lubrication or any abnormal play or wobble, and if it's belt drive also check the motor bearing.
Low Frequency Rumble from TT between songs
I'm sure it's in the songs too but I'm getting low frequency rumble now that I've switched from Harbeth 30.1s to some large base reflex studio monitors. Between songs and on the lead out groove I'm getting a rumble at mid to high volume. Is that an isolation issue or something else. Table on a wall shelf, about six feet from the BACK of the left speaker, so I'm not understanding why this would happen.