I'm not sure about mechanical valves, but with my tissue aortic valve, they (several cardio's and surgeon) all have told me that I have a minor murmur, and that this is common with prosthetic valves. As long as it remains consistent, no worry. That is why I stay with the same doctors - they actually keep notes on what my murmur sounds like so that they can verify that nothing has changed. Of course, the annual echo helps, too.