One of my garage doors has suddenly started making an unusual noise when raising the door. It still works fine, but I'm guessing from this sound that won't be for long. It's an Overhead Door opener and it's only about 5 years old. It's belt driven and the tension on the belt is the same as on my other door. I've visually inspected the door itself, the rails, the belt, and the belt guide, and everything appears normal. I lubed the door itself and the rollers about 2 years ago. It's hard to be sure where the noise is coming from. I think it's the motor housing, but the sounds gets transmitted through the door so it's hard to be sure.
My question is, has anyone heard a noise like this before and can suggest where I should look before I spend money on a technician? I've included a brief video so you can hear the sound. The sound I'm asking about is the rhythmic thunking or banging. The video is just for the sound and contains nothing of visual interest.
UPDATE: I followed the advice @Jasen offered in his answer and disconnected the door from the motor. The sound is coming from within the motor housing, not the door.