I second Grigg on making sure you stick with the recommended Lube in everything.
Do you have much room between the auxiliary and the floor to put something above it and below the floor? I know they make some spray on sound deadeners that are supposed to be pretty good. If you were to spray one of those on the underside of the floor with perhaps another shield layer added above the transmission (Similar to how a heat shield would be installed) also with undercoating sprayed on it you might get quieter.
I looked at a 3M product.
3M product info -it states "Significant reduction of chipping and road noise"
How did the install end up going? Were you able to get the angles pretty close to recommended? If you get a chance and are able post a few pictures.
Tad
