What is going on here with Boss NS2 noise suppressor?

Telejester

I bought a used NS2 and I connected it to my pedals using 4 cable method. When I start playing the volume  is real quiet and then it increases. Notes on the lower strings are much louder than notes on the higher strings for some reason too. I took my compressor out of the loop on the pedal thinking this was the issue. It wasn't......anyone have an idea what could be wrong ?

ICBM

Sounds like it might be self-oscillating at high frequency. They can sometimes do that if there’s too much gain in the loop - what pedals do you have there? Does it work OK if it’s at the end of the chain with nothing in the loop?