Well darn... I just got around to opening the 21" display. I removed all the boards and looked them over. Everything looks to be in order, but I still need to test it with a multimeter (which I lack until the fall semester at my school starts) 
maybe I could find replacement boards somewhere...
My sister said that the popping/cracking sound the 17" display would make came from an area around the yoke assembly. That's a little bit of info that throws me off. I know that the video board is right behind the yoke, with a smaller separate part connected directly to it. I've heard that there could be a problem with the deflector board from my Internet research but, being the wuss I am, I'd prefer not to mess with the anode or the transformer. Sure the 21" hasn't been used or even plugged in for a few months, but I know that they can still hold a charge.
maybe I could find replacement boards somewhere...My sister said that the popping/cracking sound the 17" display would make came from an area around the yoke assembly. That's a little bit of info that throws me off. I know that the video board is right behind the yoke, with a smaller separate part connected directly to it. I've heard that there could be a problem with the deflector board from my Internet research but, being the wuss I am, I'd prefer not to mess with the anode or the transformer. Sure the 21" hasn't been used or even plugged in for a few months, but I know that they can still hold a charge.