i can see there is a bit of a wobble in the edges of the screen where it's bright, which is not uncommon, it's called blooming. not too much you can do about it. i would also replace the caps... if your hearing popping, it could be a capacitor that's shorting out.
flybacks usually fail CATASTROPHICALLY, if it was the flyback you would be shorting out on the neckboard between the focus and ground or possibly inside the flyback, it would be making lots of noise. i don't think it's your problem. the flashing your seeing, is the voltage from the flyback getting dumped into the tube when the power is cut. if you pay attention, nearly all tv's do this when you shut them off. (they flash white for a split second.)
a shorted cap will load the powersupply down untill it does an auto-shutdown