3D printing forums

The parts of your model aren't quite lined up: It could be getting caught when it attempts to print juuuuuust slightly further around than the main section.   Also at the top, there's a small gap between the ring and the area surrounding it: It's because the ring is "rounder" (has more segments in its circle) than the model around it. The same applies to your coloured sections: Hard to see (so I added a highlight) but there's also some sections where the difference is enough that there's actually a gap between the two:   There's absolutely no way I can say with any certainty that's what your problem is. But it definitely doesn't help. If it's trying to extrude slightly out of position relative to what's already there it could get a, especially if it's priming itself as it gets there.   (Mod tip: you should probably edit your first post to change the title to something like "big blobs at colour change" or something like that)

It'd be awesome if you could attach a Cura project file (.3mf, get it ready then go to File > Save Project) of a print that has this problem so those of us with too much free time who hang around here could have a look and see if there's anything we can find that'd fix it.

I've only done bearings on UMO and possibly UM2, sorry.  But for those it was 4 screws holding the bearings.  Try google?   The thing is, if you remove the z screw, then you can test the bearings by just sliding the bed up and down.  It should be obvious.   Also look if the Z screw is crooked - shaped like a curve.   The z screw is triple helix so just measure with a ruler 3 threads.  Or measure 9 threads and divide by 3.  

Anything over 8 is a problem.  calibrating the lift switch is a complete waste of time as long as noise is at 30-60. Whether the cores are even installed or not should have nothing to do with the noise.   You need to fix the noise level first.   Do you have sources of EM noise nearby?  Sources may include: computers motors fans air conditioners speakers things with computers in them like toasters, microwaves, cell phones, laptops, unfortunately everything these days has a computer in it. wifi access points wires that lead to any of those things - even a 30 foot wire that leads to a noise source - the wire can act as an antenna if it passes near the printer   Move all those things 3 meters from your printer and see if that affects the noise.  If not, move the things where they were as they weren't the problem.   30-60 is crazy high.  I didn't know it could go that high!

Have you tried saving to the hard drive and then coping the file from there to the SD card? You could also try formatting the SD card.  They can develop corrupt memory sectors and those areas can't be written to. If you go for fomatting, remember that it will wipe out all files on the card so back up any you want to save. (If there is corruption on the SD you might not be able to get your files off it.) What printer is it?  Some don't like file names over 16 characters and others can't handle large capacity memory cards.