Vinyl and subwoofers

If the sub is working OK with other sources, I suspect the problem is most likely a less than optimum TT set-up.  Might not be well-isolated.  Might have motor noise breaking through.  Belt tension off. 

Though the ARC PH8 is a pretty good phono stage, you might be getting noise from that unit.  Bad tubes, power supply problems, other issues? 

It could also be that the phono stage is picking up noise from your DAC, computer or digital player.  There's a lot of gain in your phono stage.  Wouldn't take much to introduce noise into the signal.  Might be breaking through inadequately shielded cables.  Try playing vinyl without any digital devices operating. 

Possibly try testing the phono stage with the arm park on the arm rest.  Try unplugging the table and seeing if there is noise coming from the phono stage.  (it's loaded so that shouldn't be an issue.)

A second thumbs up to the kab rumble filter.  If your cartridge  is picking up low-frequency feedback it will double in the subwoofer and make things really muddy

Thanks tons for all the responses. I have room treatments, a power re-generator supplying clean, constant 120. A Thiel PX02, a passive integrator tailored to the 3.6. My CJ pre inverts the phase, so I switched the red and black at the speaker terminals. I'll try to be more articulate in describing the problem. A scratch on a record or the end of a record will turn into a thump, which is then magnified by the sub. This is not the problem. However, on those records that are poorly pressed, there is sometimes a gravely sound and on some occasions, this gravely sound has a bass component that is amplified by the sub, turning what should be tight bass into extremely bloomy and unmusical bass, which then muddies the music. Back in the day, 35 years ago...when I thought that putting a penny on a headshell might help get more music out of the grooves...I might have damaged more than a few records. If the sub was not there, the gravely sound would still be there, but easily overlooked without the sub. I'm going to recheck my turntable cartridge setup and look into a rumble filter, something I didn't know existed. Thanks in advance for future responses.