Rapid pulsing/ throbbing noise

Hello, I recently made my move to SC and finished my set up in my new place.
I encountered a rapid pulsing/ throbbing noise in the phono section in my right channel only. This noise is only at very high volume and the only way I can hear it is to turn my volume up most the way (at about 4:00 position) without a record playing. Now I never listen at that level (max about 12:00 - 1:00) but nonetheless, it's still there and never was before. All I did so far was to change the interconnects and ad an additional grounding wire from my pre amp to phono stage. Any clue as to what might be causing this?
If your phono stage, (or preamp) is tubed, it could be a tube?
It could be the beginning of feedback.
You may want to list your system.
Sorry I left out all so important information. It is an all tube system, Art Audio
amp, pre amp and phono stage, VPI Aries 1 TT with Dynavector XXmkII cart and
Zu Definition IV speakers. One of these days I'm going to get my system posted

Raymonda- feedback on one channel only?

Today I will start swapping out tubes, I'm guessing starting at the phono amp?
Sounds like motorboating. Probably a bad tube.
Are you near to anything with a switching power supply? Some circuits can pick up switching noise. Try the simple test of moving your phono stage and/or linestage/amplifier with respect to any other electronics in the room. If it gets worse or better, you at least can know how to minimize or eliminate it, even if the cause is never certain.
Rotating my phono amp 90 degrees in order to reach the IC connections in the back cancels the noise totally. But as soon as I rotate it back to the original position the noise comes back. I tried moving cables around (best I could) one at a time, but this doesn't help.

Lewm- what do you mean by a switching power supply? Would my Silver Circle power conditioner qualify as one? If so, my phono stage is on the shelf directly above it.
No feedback would occur in both channels....trouble shoot by swapping tubes.
Problem solved. Just a slight hiss now at full volume. All I did was switch the
phono amp with another component so it's not above the power conditioner.
Thank you Lewm for that suggestion. I'm still confused as to why that pulsing
noise was only in the right channel, but hey, who cares it's gone.
Took no time at all so I actually had time to post my system today.