Sounds like a worn valve no closing or pressure building in the holding tank if the vent is clogged. Try opening pump out deck plate and see if the problem goes away. If so the vent is clogged else time to rebuild the head.
I assume this is either a manual flush or a electric flush. If the joker valve is bad, then you might want to consider doing a complete pump rebuild. If this is a manual pump look at the rebuild kit versus replacing the entire pump assembly. I recall it being about $20 more and a bolt on application. The rebuild will still require removal of the pump AND a rebuild as well. Might as well spend a few bucks more and make the job WAY easier.
Maxum 3300 toilet issues
Linear Mode
