A popping noise during extrusion is most likely Moisture trapped in the filament causing steam to build up in the extruder nozzle, Filament gathers moisture over time, the cheap filament might have been printing fine at first, then a month of sitting on the printer goes by and it prints like crap, thats moisture buildup in the filament, even if your in a low humidity environment, it builds up over time.
As for getting the heater block tight, tightening it cold is your problem. You never replace a nozzle cold, or remove the heater block from the throat cold, or install the nozzle cold, etc. The heater block is aluminum, the throat is stainless steel, and the nozzle is brass (generally), lots of dissimilar metals with different expansion rates. The best practice when replacing a heater block is to screw the nozzle in all the way and back out a full turn, then install the throat so it bottoms out on the nozzle top end, then just snug up the nozzle. Install everything, preheat, snug the nozzle a bit again, and your good. When it cools down the aluminum contracts and it only gets tighter!
If you strip out a heater block your overtightening, and if you did it while replacing a nozzle then you should have preheated. For nozzle replacement, preheat, remove the filament, then remove the nozzle while still hot, replace the nozzle, snug it down tight but dont go 200lb gorilla on the wrench, just snug it good, then reload the filament. If done right it shouldn’t ever come loose or be loose, i print for a month or two before needing a new nozzle, and i use mostly cheap ABS filament or filament that i make myself.
The one thing that Rep2’s and 2x’s suffer from is heat creep, its well known as an issue. However since i replaced my heater blocks with the Fargo3D silicone insulated version i have had zero heat creep issues. I did also replace the fan FET on the mightyboard for a higher current version and put a slightly higher airflow fan on. The original is maybe 7-8cfm, my new extruder fan is more like 12cfm by the rating, but it seems to be moving a ton more air then the original stock fan. However, bigger airflow fans can’t run, or won’t run for long, on the Rep2 and 2X mightyboards because they will blow the fan FET with the higher current demand.