New bike and this week I seem to get all the complications.
:-)

Back wheel --> when it turns/spins, it makes a knocking/tapping sound, once per revolution.

At first, it sounded like wheel/rim hitting the fender/mudguard or the brake pads, but I don't seem to be able to locate it.

The sound/tapping can be felt through the frame (back triangle) too, once per revolution - the effect gets worse if the bike is held horizontally, so that the back wheel spins horizontally. Also, no obvious wheel lateral movement - quick release lock seems tight enough.

Has something come loose a bit and should be adjusted? - this is a new bike, used for commuting before sunrise!

Many thanks.
Archie