VPI 10/VPI MK IV/Grado Reference HELP

Three immediate things to check:
1. make sure TT ground is connected to good ground point;
2. make sure preamp ground is good;
3. make sure that interconnects are solidly seated.

If all this checks out OK, you may have a ground problem with the cartridge.

Agree. Make sure all the cartridge connectors are firmly seated, too.

Don't know why,but my table is quieter without the ground.

Is it a HO version? 4.5 mv? The Grado HO are known for this but usually at the end of the LP before it starts.I have a minor hum then but it has never been audible during music.Im not familiar with your table but if the motor is not under the platter than forget what I wrote above,its something else.If the motor is below the platter aluminum foil applied under the platter has been reported to eliminate the hum.All I can offer you,sorry...

Try reversing the TT mains plug in the socket. May not do anything, but worth a try