Failing y-axis home with loud rattling
From your video, it sounds to me as though the stepper motor is fighting against the bed movement. That would indicate to me the bed rails on the X-axis are not square to the bed movement, which would cause binding of the linear bearings on the bed.

To see if this is the issue, loosen the threaded rods in all six places (three placed times two rods). Loosen the belt tensioner so it is not causing any issues. Then see how the bed moves. If the bed is freed up, tighten the nuts on the threaded rods two at a time on the same plane (each plate of the frame). At each tightening, ensure the bed continues to move freely. Measure the distance as accurately as possible to ensure the frame continues to stay square and are parallel to each other. Once you have tightened all of the nuts on the threaded rod, then re-tighten the belt tensioner.

If none of this solves it, it could also be an issue with your linear bearings. If your Anet A8 is a Chinesium clone, the bearings are not what I'd call "top notch". I replaced mine with Igus Drylin bearings and have not regretted the $10 investment. There are other printed options you could go with as well, which you can find on thingiverse.com.