Over the last week or two I have a Squeak/Thud noise coming from the rear, It happens when I put the car in gear (Mostly just reverse but sometimes in drive) and I also hear it when i hit a bump or pothole...

I tried to find it the other day by moving the car up and down by putting weight on it and I also tried to grab things and try to move them (shocks, sway bar...and i can't get anywhere with finding the noise.

I dont think its brake related, it sounds to me like something suspension wise and definitely is coming from the rear...any ideas of what to check or even how to?

The first thing I would do is try and grease the rear ball joints. Also check the rear strut mounts as well

While you are under there..inspect the sway bar end and center links.