I have a problem with the screen on my CRT iMac: it's sort of wobbling/shaking ever-so-slightly! Any ideas to what this could be? Is it serious? It's sort of like the effect when you have a cellphone call coming through (the way it distorts the screen). I'm beginning to get worried. I bought the Mac out of PC World and got a 5 yr warranty, can I still get it fixed even if the receipt is lost, i.e. will they have my details on record? Thanks.