I have never heard of this and a quick google suggests that it is not common. Is it timed with your heartbeat or do you think it's more related to your digestion or something else entirely?
When I take my migraine drugs sometimes I get a "whump whump whump" in my ear that I believe is timed with my pulse. I have read that because blood vessels are narrowing in other places (the drug is designed to make the blood vessels in my brain narrow, but it affects all blood vessels), it actually causes the ones near my ear drums to expand/have higher pressure, making me more likely to hear my pulse. Bizarre!
If you're worried about it I would ring the doc who prescribed it. I hope you get it figured out.