Noisy brakes suck, but the fix is usually easy.
The grease is bullshit. If you do a brake job correctly it's unnecessary, and you run the risk of it fouling your pads.
Make sure everything is clean, pad pins, abutment clips, caliper bracket, etc.
Did you keep the factory shims on the back of the pads? Is all the hardware intact?
If you put new pads on the old rotors and they aren't the same friction material (ceramic/Semi-met) you will get squealing.
Like he said - If you buy new pads, get good ones, maybe spring for rotors too. Buy quality, don't buy garbage.
Try and do a bed-in procedure and get a good pad transfer onto the rotor surface.
My preferred method:
Find some open space where you won't run into traffic.
I prefer to drive with my foot lightly on the brake until the pads get HOT (you will smell the pads) The several "50-0 stops" is good too, I like my way.
Now drive around all slow until everything cools down and then test for performance/noise.
DO NOT come to a complete stop with your foot on the brake until everything is cool (this is why we're someplace away from people)
If you stop with your foot on the brake, you will make the problem worse by cooking the pad to the rotor.
DM if you have questions.
20+ years as a brake supplier/manufacturer/technical writer @ Centric Parts/Stoptech.