I've heard some say they had problems with the EZ lube zerks on the axles. I for one, have not. But the first time I did mine it took darn near a full 14 oz tube for both sides. This year, it only took a few pumps for grease to start coming out. I'll use the EZ lube zerks again next year, if no problems, but after the third time, I will pull the wheels and bearings, replace all the seals, check the brakes and hand grease the new bearings.
As for the center track lube; I just pump until some starts to come out of the ends. Took quite a bit the first year too.
Don't forget the corner springs or spray some WD or other lube onto the bottom of the motor assembly.
Is the popping noise coming from the corner posts? Need to add some dry lube (or whatever you prefer) to the corner posts.
Here's some info at this post...
12v motorized folding camper winch