Weird noise between only 1/3-1/2 throttle

[kylejj]

View attachment IMG_0107.mov

 

[tphoyt]

Run with the cowling off and see what happens or what you can see and hear.
Are you throttling up and down or is the motor doing it by its self?

 

[flyingscott]

Sounds like a rough transition between 2 and 4 cylinders.