My thoughts on the problem would be this order.
1) Improper or floating grounds/signals, double check all your solder joints... a cold solder will make those effects
2) Scanrate... too fast of a scanrate/angle will cause those effects
3) Power... flaky power lines also cause similar problems.
4) Bad setting on amps
You may want to check your scanrate and angle first as those are the easiest to verify. Start at 8k and see if things look
saner. You may also want to reduce your scanangle. If it looks sane, and just starts to linearly tweak out after you
start increasing speeds, it could be a amp tuning issue.
The other note is that there are full adjustment pots on the scanamp, but I strongly recommend against touching them
until you can confirm your laser board is putting out a sane signal.
Can you post a pic of how you wired up the board to the scanners?