Strange Grounding Problem?

I have a unique grounding problem unlike any in my past experience.

I'm using a pair of the latest NuForce Reference 9 amplifiers and a dbx 14/10 equalizer that has a two prong AC plug with a floating ground. The NuForce amps and preamp use 3-prong grounded AC plugs.

I have a kind of low-level spitty high-frequency noise in the left speaker when using the dbx. It is audible a few feet from the speaker if you listen on axis. It can't be heard at the listening position and doesn't affect the sound quality, but I'm a nit-picky kind of guy.

If I turn the left monoblock on first, there is no noise, but when I turn the right amp on, the spitty hissy noise appears in the left channel as soon as the relay kicks in. There is no hum, so that's not an issue. Even more oddly, if I turn the power off on the EQ the noise gets louder and can be heard in the right channel as well. If I unplug the dbx the noise diminishes. If I bypass the dbx EQ and hook my solid-state preamp directly to the amps, both channels are stone dead silent. Problem is, I have a broad bass peak in my room at 125Hz and I need the EQ for the system to sound natural.

I was thinking of buying a Behringer EQ, which should be more quiet, but I'm not convinced it would sound as transparent as the dbx. I was just wondering if anyone has experienced this type of odd problem and if it could be easily resolved.

I switched the amps from left to right and that did nothing. I also tried grounding the dbx chassis and that did nothing. I use a PS Audio UPC-200 power conditioner and my AC power is relatively clean. I must be missing something, but I'm not sure where to look at this point. The only thing I'm fairly sure of is that the problem is somehow centered on the dbx. The negative sides of the input/output jacks are linked to the chassis by small capacitors for RFI rejection, but I don't think that's the problem. Any help or insight would be appreciated.