Ground loop.

Are the 2 racks powered from different outlets on the same circuit? different outlets on different circuits?

Are these circuit/s on the same phase of power??

Answer these questions and you can find the problem.

Usually, it's because the outlets powering your racks are on different phases of power within the electrical panel. If that's the case, the electrician should be able to move the one breaker so they share the same phase.

But, it could also be cable company not grounding their service at entry to the home/building. Are these at play too??