Strange Noise from Underneath

[Tattybogle]

Thanks for both contributions. I THINK I can feel it as well as hear it, but I have always been sensitive to mechanical irregularities and cannot be sure.
If I didn't know better, I'd suggest it was a tooth jumping in the diff, but I am sure it cannot be that as it would happen more often and not be just the one tooth. I've never heard of that happening anyway.