Studio Preamp making noise- do i need a cap job?

[illswando86]

My Studio Pre produces a very noticeable noise. It's a low tone and sounds like ground hum, but I've taken measures to ensure I don't have a ground loop. I run it into a fifty/fifty. The noise stops when my preamp is off. I've tested my tubes. Could a cap job possibly cure my problem? Full disclosure(if this makes any difference) I've had issues with my effects loop. Running both channels with nothing in the loop, sometimes one side would drop all bass frequencies. I talked to mesa and they said that it happens when the loop jacks aren't cleaned. They told me to run a patch in the loop. I currently don't have an a/b/y box to split the mono send to the A and B returns, so I'm only using 1 channel for the time being.