No and no.

Noise supressors usually don't help with hiss. Wait - make that never. Grounds either. You're applying fixes for engine/alternator noise to a noise floor issue - different beasts.

Is the volume level of the iPod when you switch to it similar to the level of the tuner and CD?

You might want to post your question here for Tom: http://www.bimmerfest.com/forums/showthread.php?t=94915