Turntable Hum

Try disconnecting things one at a time. Grounds can be funny. Normally you want to connect the turntable ground to the phono stage. But I went to a new arm where it was the other way around, going silent only with the ground disconnected. 

First I guess start with disconnecting phono stage from preamp. Then work your way back. Connect phono stage only- turntable disconnected from phono stage, phono stage not even plugged in. Then plug in phono stage. Then turn it on. One baby step at a time. Then connect turntable ground. Then R channel. Then L. 

I doubt it is internal arm wiring but if there is no hum until you connect a phono lead then it could be. But check the individual cartridge connections first. I doubt it will go that far. This is just to give you an idea how to track it down.

Did you change anything in your system or room right before you noticed the hum? 

I had the same problem. try moving around the RCA cables around while TT is on. Do you hear a change? Try moving TT to a different position. Something inside my wall was causing interference with my TT and cables. 

@noromance I did ground lift the TT motor & pulled everything in strips out 1 by 1 , no success

@millercarbon I'll try your suggestions, the only time the hum goes away is when the phonostage is out of the loop 🤷‍♂️

@femoore12 I did add a Marantz 2270 receiver recently but nothing inputted , just plugged in and I think I removed it to see , no change . 

@ei001h I moved TT to the floor , no change , I'll try the cable jiggling. thanks 

I had a similar problem with hum like what the OP described. Tried all the usual grounding tricks. They helped somewhat,  but just couldn't eliminate the problem completely. 

Then I was given the suggestion to change turntable power supplies. Turns out my tt came with a cheap switching wallwort power supply.  All I had to do was order another wallwort power supply, only this time went to a linear type.

 Cost, 15 dollars. And voila!!! Hum totally  disappeared.  Not sure if it will work with what you have, but worth a try if your tt has a cheap switching power supply.