I would not give a brain tumor a thought. I would however, get your blood pressure checked. Sometimes high BP can cause these kinds of symptoms.
Extremely highly unlikely.
Such "thumping" or "butterfly-in-the-ear" feelings aren't uncommon; it could be just a twitch of the stapedius muscle in the middle ear (or is it the tensor tympani...? can't remember).
If it doesn't go away, mention it to your doctor. But don't worry about a brain tumor.
Best wishes,
Nancy T.