Horse burping?

[Frank and Shannon Field <field@azstarnet.com>]

I have an unusual problem that isn't really an endurance question, but
I'm concerned it may affect my horse's future health, which of course
would affect my ability to compete.  He makes a strange burping/growling
sound when cinched and lately during grooming.  I'm noticing it occuring
more and more often and can't determine the origin.  I wonder if this
means he could be sucking air?  The barn manager says she will watch him
closely for cribbing tendencies, but she doesn't think it's cause for
alarm.  She says she had a horse who always "burped" and he was never
sick a day in his life.  I cannot find a single thing on this on any vet
sites.  Has anyone experienced this?

Shannon