The Hewlett Packard LaserJet P3005 commonly suffers from noises from the back of the printer. These can range from a rhythmic rumbling noise to a loud grinding or clicking noise. It’s caused by either the fuser or the fuser drive gears.
If you get a grinding and knocking noise from a HP LaserJet 4250 or 4350, the problem is the swing plate assembly and / or fuser. The swing plate assembly is a metal bracket with two plastic gears on it and drives the fuser.