So I have the SVP-PRO pre, and I run with a Carvin 1500 amp. Going direct out to the PA, now with powered subs, I hear this annoying hum, more so than a hiss. Is there a fix for this, or is this tha nature of the beast? I've heard somewhere on this forum it is a problem with older models? (It is about 2 years old.) Is this expensive to fix? Any help is appreciated.