AD2 outputs VERY "hot" (aka: loud) for some dagned reason.
In the Console View select ALL the active audio output tracks that are accepting signal from AD2 (in Sonar they are called "Instrument" tracks), hold the Ctrl key on your keyboard (QWERTY keyboard that you type with... not your MIDI controller) and turn down the "Gain" knob of one of the track strips (this will be at the very top of the track strips). The gain knobs for all the selected tracks should turn down simultaneously.
Alternatively you could do the same thing in the Track View by selecting all the same tracks as before, holding Ctrl and lowering the Gain slider control on one of the track's (you will need to have your "Track Control Filter" set to "Mix" to expose the Gain slider).
You could also turn down the volume faders inside AD2 as well so they don't output as "hot" but I usually just use the Gain control in the Console view.
If you are expereincing WILD level fluctuations though this would be due to your "Velocity" settings for each Step Sequencer pattern so read up on the Step Sequencer and how to adjust note velocity levels.
It could also be you have manged to accidentally insert some kind of Volume/Gain envelope on the track somewhere that is turning the volume/gain up and down in an undesirable fashion... but that probably isn't it.
Cheers.