Nuforce STA200 issue. Rumble every couple minutes

Does it exhibit the problem with no input connected? Have you tried it with another source? Could be an issue with your preamp.

@dspringham i might have found the issue. 
 

it either doesn’t like my preamp or my subs connected to speaker terminals. 

I went straight from DAC to amp, controlling volume with my Innuos. And turned my REL subs off (they are connected directly to my speakers post along with speaker cables). I never had issues like this with my tube preamp and tube amps. 

gonna test with subs turned on next. Then test back to preamp with no subs. That should test all possibilities and tell me what the Nuforce likes/doesn’t like

In my opinion the STA200  is aa perfect match for a passive preamp. It is highly sensitive (350mV), very high gain unit. I own one. 

It did not work with a Joilda tube preamp I once used. A low gain  active SS pre may work.

I’ve had 3 over the years, though match could be difficult, never any problems...always worked well with passive pre, and for me a great match with Schiit Freya S preamp...and low efficiency speakers

Thanks @mesch 

I was just using it as a 3rd amp for when I don't want to burn my tubes 8hrs a day... so I don't really want to build another system around just this amp... it's very good. but with my current configuration is not a very good fit for it, 96db speakers... there's more hiss than I get from my tubes amps.... 

Great amp sound, but not a particular good fit for more all around setup.