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.)
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.)