Earth Lift Resistor

I have a tri- amped system. Hum, though low, has been a problem. I have almost eliminated it entirely through the use of earth lift resistors.

However, recently I have been advised that this is not safe. I would be grateful for the comments on the following:

Q1. Is it safe to put a series resistor on the mains earth?

Q2. Is 100R any safer than any other value?

Q.3 Is a WW safer than any other type? Is 3W WW the best rating?

Q4. Is there a safer way to fit an earth lift resistor to the mains?

Q.5 Is it more dangerous because I have these in many components in the system, not just the amps?

Q.6 Can the chassis go 'live' with earth lift resistors?

Thanks in advance.