My husband experiences the same thing, and it is acid reflux (GERD). He takes a generic "acid reducer", it has helped but he still has it once in awhile. One thing that helps him is to stand up while experiencing this, he belches and it's over.
The discomfort you're describing does sound like it could be associated with acid reflux, even if you don't have the other associated symtpoms. Have you tried a course of acid reduction medication or been scoped to make sure that there's no damage, or that there's no obstruction in that area of your body?