You may be experiencing an earth loop through the signal chain.

USB is a current loop standard: 2 wires are 0 and +5V, the other two are the current loop signal path, if the 0V is also connected through to the signal path earth/ground connection (unbalanced -ve/earth or balanced shield) through the Presonus then simply disconnecting elsewhere in the signal path (lift the shield at one end of a balanced connection?) should eliminate the noise.

PC's are a dreadful source of noise... Of course there are a couple of assumptions here that may not be correct...

I can't see whether you said or not, but if the DAW is a notebook some models (as in my HP) have the earth from the mains connected through the charger into the ground plane of the PC. Disconnecting the charger from the PC (so it's running on battery) would eliminate the noise if that is the source.

Also, CFL lamp replacements are still Fluorescents (as I'm sure you know). I've found that LED's are far superior, but you usually need to shop around to find them at a resonable price, retailers are still price gougeing on them frown

--=-- My credo: If it's worth doing, it's worth overdoing - just ask my missus, she'll tell ya laugh --=--
You're only paranoid if you're wrong!