Yeah, it's happened to me a few times too. There was one time on an elevator a woman piped up, "Someone's got a loud watch on." Just then the doors opened to my floor and as I stepped off I turned to her and quietly said, "No, that's my heart." Silence...
The first night I was home from the hospital my husband and I were laying in bed and he said "Man, my watch is-- digital?" It dawned on him mid-sentence that it couldn't be his watch and that it must be my heart. I've gotten the watch comment more than once. The best was when I was visiting a friend in West Virginia and no matter how many times I told her it was my heart she kept insisting that it HAD to be a watch. I finally held up my watch and showed her there was no second hand... Later, when we were out of the car, I let her put her ear to my chest and she was finally convinced that the sound was, indeed, my heart and not my watch.