HP Laserjet 4250,4350,4345 noise

This may be caused by a loose clamp that holds the fuser assembly firmly in place inside the printer. (speculation on my part)
When the fuser gets loose, it falls away from the printer ever so slightly and the gears on the fuser are not flush with those of the printer. The teeth of the gears skip and cause the horrible grinding.

This may produce paper jams as a consequence as well as sounding awful.

You can place a pad of some kind (I used 3 square post-its, each folded over 4 times for a total of 48 paper thicknesses, you may need more) on the rear door on the left side so that when you close the rear door the pad will press against the left side of the fuser and the gears will push together more closely and the sound should stop and paper jams may be diminished or eliminated.

It may be easier to attach the pad strategically if you remove the rear door first. There are two flat, postage-stamp sized surfaces on the rear door and the fuser that come close together when you close the rear door. This is the area I used to affix the pad. (this is done by squeezing the sides of the rear door inward to disengage a peg from a mounting hole inside the printer.)

Once you figure out what I'm talking about, the repair takes 5 minutes and 5 cents.

Awesome!

Here's another that costs a tenth as much with a 6 month warranty. Found it on Froogle.

http://www.pinnaclemicro.com/compu [...] 1-0043-000