What firmware are you running on the board? If it’s Marlin, that’s likely the problem - it’s a relatively terrible choice for lasers at the moment. It’s improving, but when compiled for 3D printing, there’s a few things they do to the fan outputs to reduce power surges when the fans turn on, and that makes them unsuitable for use with lasers. You’d have to figure out how to recompile your firmware with the fan soft start disabled and the PWM output updated more often - I think the default is 10hz, and it needs to be at least 1000hz.
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