OK, this is a little funky. It made me think of Rob and his mystery noise a few weeks ago.
A few days ago, while shaving at the bathroom sink, I hear a light, rapid, dripping sound. I can see that the drip isn't from the sink faucet so I check under the sink and the shower, no drips there. OK, maybe it's the toilet, nope. WTH!!!
With everything else I need to deal with at the moment the mystery dripping noise goes to the bottom of the list and I move on.
That night while in bed I hear it again so now I'm getting a little pissed and search the bathroom again. After giving up and going back to bed I can tell that the noise is more rapid than before my search. That's when it all came together. I've been looking in all the wrong places. The noise isn't external, it's internal!
I can hear the new mechanical heart valve open and close!!!