Replace my EAR 834 P with volume control for EAR 88PB.


Hello everyone. Just direct replace EAR 834P  for EAR 88 PB. When volume control set to 0 (left end) speakers pick-up the hum, when turn a little up (just a very little) up hum disappear , and everything become fine, sounded just super. What can be wrong in setting or maybe something inside the box.? Thanks in advance

yarom