Did you set up the Carter pump with a return line to the tank? Not sure that it would help with noise, but I have heard that the rotary pumps do not like having their output shut off (by the float valve) and need to have some flow all the time.
When I installed one of the rectangular Facet pumps (which are also pretty loud) in my Stag, I used a double isolation mount, which worked out pretty good. Rubber mounts from the pump to a separate plate, then rubber between the plate & body. I can just hear the pump from inside the car with the engine idling, but not once I get moving (and I don't usually notice it at all).
Of course you could always convert back to an original type mechanical pump. They're quiet