Occasional monitor flicker

I've got a recent problem with my Sony 200ES monitor, which has been
working fine for ages.

Ocassionally, i.e. once every 15-30 mins during use, it flickers, as
if the power has been turned off for half a second and back on again.

I also notice something else when I shut down the PC, and the monitor
goes to standby: I hear the quiet 'crackling' of the static for a few
seconds as normal, but then the static sound repeats, several times. I
now switch the monitor off to avoid this, but I have a feeling it's
unwell.

Any advice? Do I need a new monitor?

Pete