Dreamer grinding, gear slipping?

Really at a loss here...my Dreamer started grinding terribly when printing and I can't pinpoint what this noise is. You can hear it at the 24 second mark in this video.

At first I thought that the print bed had somehow raised above the level of the nozzles, but that's not it -- I lowered the thumbscrews until the bed was well clear of the nozzles, then leveled. It doesn't appear that the nozzles are touching the glass.

Any pointers would be greatly appreciated; I'm not at all comfortable running the printer when this is happening.

Okay, discovered one new thing -- the printer seems to have lost track of where the 0 is for the Z axis. When I give it the Home command it moves the head to the back right corner and the bed to Z = 0. If I use the jog to move the head back out toward the print head, though, the nozzles run into the side of the bed. I'm not sure how this happened, nor what to do about it.

Trying to think of what can make that noise. There aren't any "gears" in the system, just belts and pulleys. I would check your pulleys to make sure the set screws are tight, then adjust any belt tension to rule all that out. Threadlock the set screws in the pulleys. Usually a loose belt would slip on a quick move and it isn't trying to do that.

One thing I I see is that your platform is moving from side to side, this makes me think that you are not hot enough for the extruder and it is is leaving a rough surface for the nozzle to offroad through.

Yeah, "gears" is my general word for "don't know what's inside this machine, but something clearly ain't right." I think it has something to do with the height of the platform -- when you send yours Home, does the platform normally rise high enough that the nozzles will run into it?

No, the platform should not rise enough to hit the extruders. The Z limit switch should be triggered and set the home position correctly to clear the extruders assuming that you have leveled the bed properly.
Adjust the bed down with the leveling screws to be sure the extruders will be clear and home the machine. It should go to the far right corner and then raise the platform until the limit switch is contact. It should then move down about 10mm and move back up slowly to the switch. If all this happens, then follow this by leveling the plate which is when the actual extruder to plate distance is established. Could these screws be working loose and letting the bed rise?

My Dreamer has lost position when the firmware bug that disrupts printing on loss of communication (e.g. closing Flashprint when the WiFi is still connected) manifests itself.
When I forget and a print fails, I press the processor reset button before resuming and this has avoided problems with the loss pf position.

With regard to the noise - my Dreamer makes a noise when the platform goes up or down near the middle of the travel. The metal platform is actually rubbing on the plastic wiring loom that runs up the center of the back wall. The noise sounds much worse than it really is but I still don't like it. I have tried manipulating that wire harness but it is just too thick for the space allowed. On my list of fixes/improvements is to address this properly but meanwhile I just cringe when I hear the noise and keep a watchful eye on the plastic look for signs of chafe.

Just listened to your video. Your noise is not the same as my wire loom interference.

Graham

This sounds like stepper motor is skipping steps. In your case it's Z axis motor.

I would suggest check wires and connectors on driver board. May be check 24V on that big green connector (top right corner of driver board). Reconnect connectors, just to make sure they are firmly set in sockets.

PS: I had this problem, but in my case all motors intermittently acted like that. After reconnecting, resetting connectors all is good now.