Cybernetic

Obviously these terms are subjective, but this is what I "hear" when I think:
- Hum = hmmmmmmmmmmmmmmmmmmmmmm...
- Buzz = bzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz...

At what point does a hum become a buzz?

The only reason I'm asking is because one of the earlier posts mentioned these three things. The hum is associated with aftermarket HU with stock everything else. If that is the case, then I don't really have a problem and it should be resolved once I get some decent speakers and amp.

If it is a buzz (mine is not loud which means it gets hidden under music once the volume is turned up a little but definitely noticeable at 0 volume), then I have an issue with grounds* and would most likely result in me buying some ground loop isolators.

If I were to end up buying isolators, which should be good? :
PAC is expensive, but reputable?
Cheap 4 Channel GLI (for cars as well?)


*I've tried grounding the stereo ground to the car chassis, rechecking the harness ground connection, grounding the inside of the RCA to the stereo chassis, the stereo chassis to the car chassis. None of this has done anything. I'm working with an OEM Lexus ES300 amp and a Amp Integration Harness from Metra that converts the incoming connections to RCA for the HU.

EDIT: Rewording