Bits inside the rim did catch my eye.

Mavic 217’s had a weld slag/slug that would come loose and clunk, but usually at lower revolutions. Very “soothing” on slow climbs, like the drip-drip-drip of a faucet.

The welding is probably not an issue with your rims, but if something made its way inside the rim it might give a constant clunk per revolution.

John