Refrigerator problem

Does anyone have an idea what my refrig problem may be? My Domestic RM 2807 refrigerator will start (either with propane or electrical) but shuts off in about 2 hours. I can then hear a noise that is coming from the lower circuit board in the outside compartment. The noise changes when I press on the circuit board. Cleaning the venting didn’t seem to help. I’m thinking it might not be the circuit board since the unit operates for few hours before shutting down. Could something be heating up?
Thanks for any assistance.