HELP! Awful Sounds Upon Homing/Starting & Finishing Prints

[XCT357]

Hello Everyone,
So I recently pruchased my first 3D printer, a Printrbot Simple Metal from Craigslist, and I am addicted to the hobby now. It is a Simple Metal without a heated bed and a Rev. 4 board. Initially, the seller said it had issues with z-axis calibration and he didn't have time to troubleshoot, so I thought I would give it a try. I did get it to work properly quite quickly by downloading the default Start G code from github, and it prints like a charm. The print quality is good, the settings all work so far. Now onto the issues.

1. So, since day 1, I noticed that when I try to home the printer, it successfully homes, but it sounds AWFUL while doing so. It seems to me like the motors are trying to force their ways past the x/y limits and then it gives up and sets a "home". It does this every time I home, but not when I make the printer move to its extremes manually within pronterface/cura/repetier. I have noticed from YouTube videos that this is not the norm by any means. I have attached a video you can watch to see for yourselves. There also seems to be a subtle cracking noise when homing the Z axis as well which I have been unable to find a cause or remedy for.

2. The other Issue is the fan will not work. I know it is receiving power because I have tested it with a volt meter and the connection has an output of 12v. Also, the fan gets EXTREMELY hot when I send the M106 command, but the blades will not turn. I tried replacing the fan and testing both old and new with my own 12v power source and they both work great. Just not when connected to the printer. I made sure the printer is connected correctly and the wires are all good. Someone mentioned a "MOFSET". I am a beginner when it comes to electronics and I have been having a lot of trouble finding out how that can be an issue/be fixed. I am using a desktop fan now and that works perfect for printing, but I would still like to get a more direct and controlled output as far as cooling goes.

The most important Issue at this time for me is the motor issue, I want my printer to last and so far the prints come out great so I believe it is worth a try to fix. Thanks in advance for any replies. Here is a link to the video:

[curious aardvark]

your endstops are either not working or connected incorrectly.
Also try swapping the wires over on the fan connector.

I've often bought cheap fans and discovered the wires are reversed.
Because the sockets only fit one way people, tend to assume they are correct and something else is wrong.
Nope - the chinese have a somewhat random approach to 'standard' configurations.

Either that or you need a new fan :-)

And yep - the printrbots were really great machines.
Still no idea why the company went under - they sold as many as they could make and rarely got a bad review.