My hard disk (Seagate 1TB ST31000340AS) has started getting whiny (a very high pitch constant noise). Should I start shopping for a new disk now, or do you think it could last a while longer?
You should definitely start shopping...meanwhile, back up your drive if you haven't already.
That happened to me before, and the drive lasted about two weeks.
Let's think about this from a non-techie view point that most can relate to.
I am going on a long trip in my car. The engine is making a bad noise. Should I go anyway? Listen to your instincts.
If the info on the hard drive is important to you, then copy it onto another hard drive. In fact you could add a second internal or a second external hard drive and move all of your data over there leaving only your operating system on the whiny drive.
Then if it fails you have really only lost the time for a reinstall of your OS and application software. IF you are really up for it get a SSD (solid state drive) for your new system disk and your performance will jump dramatically (especially start ups and shut downs!)
Hmmm... hard drive is making bad noises... act right away or don't worry about it. Either something will happen or it won't.