The amp is not "noisy" from a spec point of view, but it can be noisy if the gain settings aren't set properly to match the guitar. When we designed this, we did alot of analysis of active and passive bass pickups, especially transients that are produced while slapping and popping, which was becoming a more popular style of the era. Slapping and popping, especially with active pickups, has huge transients that would overload the preamp section of most bass amps of the day. So, we designed a huge adjustment range for the input gain section, plus added the compressor to help handle this.
My suggestion is to set your bass guitar volume(s) as high you will would normally use, and play as aggressively as think you ever will, then adjust the input gain pot until the overload LED barely flashes. Then turn the input gain down just a touch, so the overload LED doesn't, or rarely flashes. (If I remember correctly) The overload LED has 2 detection points, one right after the input gain, and one after the tone controls. If either overloads, the LED will trigger. So, if you boost the tone controls (especially lower frequencies), you may trigger the overload, in which case you should back off the input gain until the LED stops flashing. It's actually very much like running a PA mixer channel, where you have an input gain, or "trim" setting with a "peak" LED, and a channel fader for the output..
The key is to adjust the input gain and preamp for the highest signal you can get without overloading, then adjust the master volume for the playing level you desire. This will keep the amp running at the lowest noise level.
Hope this helps.
