The mp2 has a noise floor?
There is a manual for the MP-2 in the archives section...
That said, there is a lot of debate over using the limiter on the MP2. There is basically 2 schools of thought
NEVER use it
Use it Sparingly
The never use it crowd say to either set up so you never see the peak lights (prolly a better idea) or set it up so they only occasionally come on (why you want to clip I dunno, but not going there)
The use it sparingly crowd (I am one of em) suggest setting your levels so you are as high as you can go without hitting the peak light, then putting the limiter on and enjoying the show. I personally can't hear the limiter when I use it this way, YMMV.