Litlle late for my post but here it goes.
My bet is that poofing comes from toner stack up beneath developer assy,we all know this machines as dirty litlle pigies,that's why it's random,because it drops on papper sometimes due to enough vibrations untill it piles again or another vibration erodes it down.
Remove front cower,and brown cower with mechanical counter on it,take out cassete and laser assembly,U'll see there a nice lil pile of toner on plate beneath lasser assembly and developing assembly plate,that I usualy see on theese machines with over 700k on counter.
It prolly has some toner on right hand handle when u take it out,u can loosen up the screws holding the plate that's below developer assembly,2 screws there and on a vertical plate closer to registration roller,loosen them and vacume toner there.
I think toner slips out on it's way to developing assembly via PCU,those sponges wear out over time.
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