for Laserjet 4200 4250 4300 4350 4345 series printers
If you get a grinding and knocking noise from a HP LaserJet 4250 or 4350, the problem is most likely the swing plate assembly. The swing plate assembly is a metal bracket with two plastic gears on it and drives the fuser.
The problem is that the teeth on one or both of the gears wear. You might also find that the plastic clip that holds the fuser in place cracks. The new swing plate assembly is modified to reduce the wear on the gears. It is also supplied with a modified two part spring loaded fuser gear.