This afternoon, i was drifting off to sleep & heard a weird noise (suction cup like) in both ears. i sat up & didnt hear it again. then i started falling asleep again, & i heard the noise again. what is this? & can i prevent it from happening again?

The eustachian tube helps move mucus created in the middle ear membranes to the throat. It also allows air to enter to maintain the equal pressure across the ear drum that permits normal function/hearing. You don't want it to remain closed or the system will not maintain normal function. The cure of any bothersome would depend on the cause(s) that are making this bothersome