Driver not putting out full power

Get rid of that fan. That should have been the first thing to go when you started troubleshooting. The motors on those fans are not DC motors, they are AC motors using an inverter circuit to provide the correct voltage and frequency. Whoever designed it probably assumed that the fan would not be sharing its power connection with anything else, certainly not something as ESD-sensitive as a laser diode. I think the fan inverter is back-feeding noise into the DC input line and causing the laser driver to do things it shouldn't. Only way to eliminate that is to remove the fan from the circuit.

ETA: Here you go: link. Scroll down to the section "Current draw by a DC fan motor", particularly the caption under figure 2. According to that, the inverter circuit can indeed cause ripple on a DC line if not properly filtered.

I've heard of this before. I can remember
one particular incident where a fan ruined
several whole computers before the problem
was found.