My monitor (21" Samsung SyncMaster 1100p) has started emitting a very annoying high pitched squeal. It seems to go away if I move the monitor very slightly (ie. gently, not a tap) and then comes back some time later. Is this a common issue with CRT monitors? Has anybody got any solutions or is it just a frequency I'm not meant to be hearing?

old crts do that sometimes it gets annoying when you figure out that the pitch changes if you scroll the page youre reading

anyway this is what i found
http://www.5starsupport.com/faq/monitor.htm#high-pitch

haha my old Dell used to do that. it took a while to learn how to tap it just right so the sound would stop. real annoying though.

Yeah, CRTs tend to start whining when the tube is starting to go on them. Time to start saving up for a new monitor.
Although it's pretty much hit or miss how long it'll last before it finally pops. (our last TV went within 3 months of it starting to whine, but my old 15" monitor whined for over a year before I put it up into the loft as a spare to drag out when I need it for testing)
You'll get pretty annoyed with it before very long though

Oh well only cost £12 so not too much need to save

Probably a component resonaltes. So it´s a mechanical, no electric mistake. If I´m right you could fix it by yourself if you have a little technical knowledge and some plasticspray. I will not advise you to open your monitor as it´s able to keep some very high voltages for a long time.
Just Google for "a very annoying high pitched squeal" and you´ll find out what I mean.
You should also try to change the supported refresh rate of your monitor and see if this helps.

that happens to me sometimes its really annoying and it sometimes gets really loud. i just turn the monitor off then back on and it works

It could be the "common" monitor buzzing issue which only some people can hear... and is usually related to a fault in production resulting in a faulty ground wire and/or the use of the power unit inside the monitor. Sometimes the "buzzing" can be solved by increasing the brightness on the display and then using NVIDIA Control Panel/ Windows to reduce the brightness instead.

For example, one of my monitors makes this buzzing sound when I drop the brightness to 70% whilst the other doesn't (exact same models). Easy solution, leave monitors on 100% brightness and reduce the brightness through software (Nvidia Control Panel).

I get the same kind of noise of an LCD screen, also makes an annoying buzz while scrolling. It's got 3 dead pixels too, might try that program out that's on the bottom of that page someone posted.