G-labs DVO Hum with a RV50

[SuperSpit]

Hi,

i seem to rememeber some guys round here talking about the G-labs DVO and wondering if they can help.
i came across one for a bargin price and snaped it up.
While it does what i want it to do, there is a annoying hum when i select the first channel but only in the effects loop of my RV50.
I've tried a few power supplies but the hum is still there. The only reason i want it in the effects loop is to make use of the solo boost.

anyone got any ideas?

cheers

Johnny