What's the crunchy sound?  

print

Sure sounds like it is moving the print and cracking it off the bed.  Is it moving the print at all?

No, print not moving.

The print is very solidly attached to the bed, not moving at all.  It's a long print, over three hours, and it's been making this sound the whole time. It does seem that the sound only occurs with left-right movement of the print head, not forward back motion of the printing surface.

Some tests

I lubricated the rails but that had no effect on the sound.

I created a small test object, just  a vertical cylinder (much like what was being printed in the YouTube video and which was causing the original sound) and printed that. The sound occurred again.

That vertical tube was centered on the print bed, so I thought maybe it has something to do with where on the print bed it's located. So I created another test with the same vertical cylinder but positioned on the front left corner of the print bed. Same sound.

I then created just a rectangular object, oriented so that the main print head direction (for at least the outside of the object) would be left-right and forward-back (not in the rotational direction of the prior prints) and printed that. Practically no crunchy sound. A slight increase in noise as it was doing diagonal motion to fill in the inside of the rectangle, at the end of each diagonal line.

So, lots of noise when it's doing circular motion, not so much, but still some, when it's doing repetitive diagonal motion.

Does that offer any clue as to the cause of the sound? Is there anything I should be doing about it?

Possible hot end fan noise

I had a similar crunchy sound that was the 40mm hotend  fan.  seems like it didn't like the X carriage moving side to side.  

I found it by gently touching the spinning hub to take out the axial play and the noise stopped.

illusion.

Posted by: @rogerinhawaii

The print is very solidly attached to the bed, not moving at all.  It's a long print, over three hours, and it's been making this sound the whole time. It does seem that the sound only occurs with left-right movement of the print head, not forward back motion of the printing surface.

Yup.  It was an optical illusion on my cell phone.  

RE: Similar crunchy sound solved

Posted by: @rogerinhawaii

Sometimes my PRUSA makes a somewhat "crunchy" sound as it's moving the print head.

Is there something loose? Is there a bad bearing somewhere?

Here's a YouTube video of my PRUSA in operation and making the strange "crunchy" sound

I solved my similar crunchy sound by re-installing the Noctura 40mm fan and taking out the Sunon 40mm fan that I had installed when upgrading to the Mosquito hotend.

It seems that the "red stripe" Sunon does not like rapid back and forth movements along its axis of rotation..... with the motor out the fan can be made to rattle and knock when shook along its axis of rotation.  The Noctura fan does not do this. 

The Sunon works perfectly fine otherwise.

Hope this helps!

Happy Printing