Rear Brakes Chriping like a Nest of Birds

Long post...bare with me...

I have had this problem of my rear brakes chirping like a nest full of birds twice now. It happens when going any speed, obviously gets more pronounced the faster I'm going. It goes away when I hit the brakes and you can hear it slowly get fainter when I gradually apply pressure to the brake pedal. It is very annoying and quite embarrassing...

The first time this happened (2 years ago or so), I replaced the rear calipers thinking my pistons were seized. This solved it for about a 2 years. Just recently we had my rear-end out for 4.10s and my dad painted my rear calipers for me (did a shotty job and just sprayed them while they were hanging there with the axle out which I was fine with since I wasn't even going to mess with them). Now the chirping is back.

Since then, I thought well, it's probably not my calipers so I bought new pads and a rear disk brake repair kit from Rockauto (came with new pad retaining clips, new shims that the pads slide on, and new guide pin boots, and bolts). I put all this on about 3 weeks ago and the chirping went away for about 2 weeks.

It's back again! I am lost as to why this keeps happening. The only things left that I can think of are the following:

1) Warped Rotors

2) Stuck E-brake (I do not think this is it since it clearly disengages)...although the calipers are rusted as sh*t and now painted over...lol

3) Calipers are bad again (Would not be surpised...the shop that replaced them did not use the best calipers).

4) There is actually a nest of birds that have made their home on my rear axle and I will have to deal with it accordingly...12 gauge....

Just got back from a test drive after I replaced the pads, sanded down the area on the bracket where the pads sit, new guide pins and bolts. The chirping is gone but we will see if stays gone.

Here are some pictures of the inside rotor (looks bad and I should probably replace them but im not going to), the inside pad, and the guide pin. You can see where the inside pads were only making partial contact on the rotor. The guides pins looked fine to me but I put new ones in anyway. Both driver and passenger side rotors and pads were the same on the inside. Also see where I sanded down the bracket where the pads sit (I used 60, 100, and 150 grit). I hope the noise stays away but if it does I will keep updating this thread until it's gone