A problem I discovered last night is there is a lot of noise coming from the D.I. Balanced outputs in my Ampeg SVP-BSP preamp. The BSP has 2 D.I. Outs, and they both make the same noise. It is in the same rack as an Ampeg SVP-CL, and the CL's D.I. out is perfectly quiet. I can make the CL have the same noise as the BSP by pressing the Ground Lift switch. That points me in the direction of some ground issue with the BSP. The BSP does not have a Ground Lift switch, but it sounds as if the ground is lifted. Normal power amp/speaker operation is fine, with no noise or hum at all. I'm using the same cables, power source, etc. The only thing that was different was the power cable. I'll swap that tonight, but if that was the problem, I would assume the normal operation of the preamp would have hum or hiss noise through the speakers, correct? What else can I check, or must it be brought in for service? Thanks for your help.