Apple B&W CRT monitor popping and clicking

[Ian Frost]

Hi all,

Recently booted up my B&W Powermac G3, all came up fine including the 17” CRT monitor. However after a second or so, the 
monitor gives a ‘popping’ sound and the image on the screen expands then shrinks. This repeats every few seconds.

I’m guessing the monitor is on the way out - but as this is a complete B&W system - I wondered what the likely cause is?

Thanks