I have recently acquired a VK-P10 SE phono preamp (preowned of course) and I have noise issues when switching in the step up transformers that are in it. I don't have noise when they are switched out. I characterize the noise as SNAP CRACKLE POP. I have the phono preamp grounded to the tonearm. The acceptable setting with no noise is the SUT's switched out and the gain switch set to HIGH, this yields 59 dB of gain, according to the manual, which is good enough for now. But, I would like to try MC cartridges with lower output where use of the SUT's will be required to achieve the higher gain. BTW, I am using RCA cables from the tonearm to the phono preamp's unbalanced input connectors, and the XLR shorting plugs are in place. Does anyone have any suggestions on other things that might cause this?