no, can't cite a regulation, but pull some federal parks on the net.
It has to do with if the park is considered a wilderness area and also if it has posted noise ordinences at the check in.
I suspect they enforce all park regs if they feel you are crossing their boundaries.....even if you aren't a guest...
2 other things to know
you have to have a nat. park approved flame arresting muffler on generators and motors in general
generators can't be run late at night