Is cheater plug safe with grounded monster power?

I recently plugged in a new amplifier into my monster power HTS-2600 and experienced a loud speaker hum. Applying a cheater plug to the amp outlet on the HTS-2600 completely eliminated the hum. My question--and excuse my ignorance--is whether it is safe to use a cheater plug to the amp outlet of a power station that is itself properly grounded? Although the temptation to continue using the cheater plug is high because of improvement in sonics, I am not comfortable because I think the amplifier without a ground to the power station would not be protected even if the power station is grounded. Am I correct in my logic? I thought a cheater plug was only safe when used with old 2-pronged outlets to allow use of 3-pronged plugs and attaching the cheater plug wire to the screw of the grounded outlet?