This really looks as if the preamp gain on the Amplifier was the fix, not the grounding. The only time I've heard the "Mr Scratchy Mouse & Friends" from my unit was outside the sled feeding a very high input-impedance amp. I suspect that the majority of cases where people are reporting this, they have chosen far too high an input gain to their amp.

I would be willing to bet that cutting that earth strap to the sled will make zero difference.