My Y axis was never really smooth, so I tried realigning everything, and then noticed something odd. Have a look at the video:
goo.gl/photos/wq3eWMwpPygaF4Py7
All pulleys are loose, no matter how I position them as I move the print head over the Y axis, towards the back of the printer, the X belt slacks. i can only explain this if the Y axis rods arent perpendicular? I have no idea how to go about solving this. Suggestions?
Best way to check this I guess is to remove the rods and lay them down on a flat surface and then check if they look by the eye straight.
You told that you did the alignment procedure, but did you also try to knock the clamps with a hammer or so a bit? Like you can see in the procedure on the wiki or on the picture shown below:
This looks like an alignment problem.
Have you seen this procedure?
http://www.k8xxx-3dprinters.crimed.be/w/index.php?title=XY-Carriage_Alignment
Thanks guys, that pretty much solved it.
disclaimer: I did not assemble this printer, so I plead innocence. Or ignorance 
My 8400 has developed the Y grinding noise mostly at full Y and around Home.
Loosened up everything and yes the carriage is stiff round full Y, no hammerering or adjusting seem to help. 
Help…
Perhaps check if all the bolts that hold together your enclosure are still tight, and there are no spaces between the panels (*), otherwise your rods may be out of alignment.
(*) thats what the manual says. Mine was assembled way too losely, but TBH, Im not entirely sure how hard to tighten all those bolts, there doesnt seem to be a distinctive point where its secure. I’ll also say mine is not entirely without (tiny) open seems. But tightening everything in combination with the instructions in the wiki certainly helped a lot.
A minute after writing this it solved itself!
With everything loose, I grabbed the side rods seen from the front and pulled with some force outwards, and something that was stuck…well loosened.
Hopefully thi might be of help to somebody.
[quote=“8400”]A minute after writing this it solved itself!
With everything loose, I grabbed the side rods seen from the front and pulled with some force outwards, and something that was stuck…well loosened.
Hopefully thi might be of help to somebody.[/quote]
Thank you …