Cheri, here's a thought:
Usually, if you do get any air in there somehow due to strenuous moving and a vacuum effect, I would think the air could come out without too much noise due to the hairs in the area preventing a seal from forming. Perhaps the cream stuff formed a seal of the outer lips, which caused the air make noise as it escaped.
Our "fur" normally keeps the lips from forming an airtight seal- but an ointment might create a seal despite it.
Maybe you should try applying less ointment, and applying it to the chamois instead of directly on you? Just a thought....
Obviously, also try riding without the creme and see if is still happens. Or maybe a bit of talc instead?