Thank you! Appreciate the informative suggestions!Check to make sure your condensate line is clear along with the p trap. . Any water leaking from the unit? Also if you have a condensate pump make sure that it is working. Negative pressure within the unit during start up will sometimes suck the water out of the condensate line making a burping sound.
Oh almost forgot, check to make sure your filters are clean and make sure the return air inlets are unobstructed. Dirty or clogged filters or restricted returns can make negative pressure and try to suck thru the condensate line or unit housing.