Yeah, I'm having the same problem... 3/4 are noise-free, but the main out gives me noise when the sound is activated (eg. playback, engage the totalmix output effects, all the time Ableton Live is open). No difference with/without the extension cable.
The noise is very high-pitched and tires my ears very quickly.
For now, I'll plug my monitors through the headphone jack, but this can't be a permanent solution.
oh, and just playing around with the extension, I've realized that you actually get the sound when the metal surrounding of the BO cable touches the metal of the interface connector (even if no pins are inserted and just on the outside of the connector... even just the screw hole). And this doesn't happen when it touches other metal, just the interface connection (I touched several coins to it to try).
Here's my setup, I'd really appreciate a response from RME as to whether this is "normal" and they have a solution, or I should return it for another.
M2N-MX SE
Athalon 64x2 5600+
Network: onboard NVIDIA nForce 10/100
Video: NVIDIA GeForce 210
Windows XP Home SP3
Totalmix .942
FirefaceUSB .984 rev184
Passive monitors: energy pro22
amp: luxman lv-105u
Thanks for your time.
Étienne.