So, this is probaby something99% of you know, but I'll write it here just for teh benefit of anyone who can't figure out how to get rid of noises.
We're working on setting up a computer recording station, using my old computer in a new case witha 16 channel recording interface. We got a good deal on a new Yamaha mixer, then we found 2 hardly used KRK powered monitors. When we hooked everything up there was a loud (-50db noise coming through. First thing I thought was "ground loop". So I check that everything is hooked to the same powerstrip, meaning it uses the same ground. Seems ok, but noise is still there. As I get ready to open the computer, I decide to eliminate everything hooked up to the compuetr and add it one by one until we find the noise. Well, it came backwhen the spekares were hooked up to the mixer. Even when they were off...so it MUST be a ground thing. I asked my band mate Hans if we could eliminate the grounds on the speakers, and he found 2 plug adapters that do that - presto cadabra, no noise. So, the speakers are getting their ground through the audio cables that eventually get to the computer which is grounded.
Something to look for when connecting a few grounded devices - only one needs the actual connection to the ground in the outlet.
Again, I'm sure this is no news for most of you, but just in case it helps someone...there it is as a reminder.
Ran