I believe that noise reduction may be an optional plug-in in the case of Sound Forge. It is built-in in the case of Audition.

> They use the noise sample to create the filter parameters, and give control over how much filteration is applied.


Premiere Pro has also such an audio filter. It's called DeNoiser.

I suspect that the Premiere Pro audio capability is partly built on Audition technology given that Adobe bought Cool Edit Pro a couple years ago.

I have a similar problem
 

I have the same problem using the ma-100 on my xl1. Like in your case it does not matter weather a mic is attached or not. Gives me some hard times - especially when we have a shot where a boom is needed. Cuz`then the mic-input controll needs to be turned up verry much (manually) most of the time, which makes the noise even louder. But recently I found out that the noise is much louder and more present when I´m using the 3x zoom wide-angle lens. I talked to Canon Service abuot this and they said it could be a problem whith the lens interferring with the circuits of the cam somehow. Anyway I`ll have it checked out by next week. Maybe I`ll know more by then.