Crackling noise from my Krell KRC-HR

I have the above preamp and the external Krell KPE phono stage. Lately I have been noticing a crackling noise audible at higher volume levels. This is most audible only if you turn up the volume with the phone stage selected as the source with the record not playing. The noise is not there when i select, say my CD player as the source vs. the phono stage. So one would think it's the KPE, right? Well, when I substitute another phono stage (tried a tubed Rhea by Aesthetix) I also get the crackling, but slightly different due to the tubes I am guessing. Anybody ever experienced this and if so, could it be the Krell KRC at fault?
Does the crackle occur only as the volume is being changed, or just when set to a high volume? I once had a KRC-HR that would crackle as I was changing the volume. It needed a new volume control.
If it occurs after the volume is set, try plugging the KPE into another input on the KRC-HR. That will tell you if it is in the KRC-HR line level section or not.
Since changing out the phono didn't help, I would guess that it has to be in the KRC-HR.

Good listening,
Well, finally figured out the issue after much aggravation. It ended up being the hard drive on my iMac which is in the same room as my stereo and the crackle is only audible with the phono stage selected. So, the cartridge was acting like an antenna picking up the frequency generated by the magnetic HD On he iMAC! Drove me freaking crazy, but turning off the Mac eliminates the crackle! Solution.. turn off the computer during listening sessions!
Nice! Problem solved and no stereo down time or repair!