The typical Onan fuel pump is a diaphragm type, so the clicking is the pump running. On my '02, before I started having problems, the prime switch caused the pump to click quickly then slow down and stop, indicating that the carb float-bowl had filled. The generator would then start readily.
Now, the prime doesn't stop and I get a very rich start attempt and then it runs for a couple of seconds and shuts down. I think the float isn't floating any more. Still working on the problem!
Frank and Eileen
No longer RVers or FR owners