About a month ago, I spun my car out and the rear of the car went on top of the curb. Long story short, it nearly took a 3rd of the rim out (like a big chunk is gone) and ever since then, the rear diff vibrates really hard/loud for a second or 2 then goes back to normal noise (speed is around 40MPH). It keeps doing this over and over and the faster I go, the faster it'll pulsate. Now, I already have another diff to replace it and all but I really want to know, what's causing the pulsation. It still drives fine, just pulsates.

 

Bent spline or damaged clutches from the impact.

Also after a hit like that the lower rear arm bushing get damaged, replace your rear lower alloy arm. Once damaged these lower arm bushings (where it mounts to the knuckle) can move up to 20mm in deflection causing weird movements while driving - under load (cornering) or getting light over small road imperfections.