Apple Watch random taps / vibrations

Hi,

Beginning with watchOS 3.0, my gen1 Apple Watch often taps / vibrates when there is actually no notification - usually if I stand up from sitting, or start moving.

I've not been able to find any setting to turn this off, and have found no other examples via Google. Am I the only one this happens to? Does anyone know why it is doing this, and how to stop it?

Thanks,

James.