A crackling noise, when you adjust the volume, is due to a defective potentiometer. (That's the thing that the wheel or slider is attached to). A quick squirt of switch cleaning fluid, e.g. Servisol Super 10, will often fix the problem. It's �4 per can
http://www.maplin.co.uk/Module.aspx?ModuleNo=4 153&criteria=switch%20cleaning&doy=26m9
but, if you know anyone who works in electronics, you might be able to get someone to donate a free squirt.
If you can't get hold of the proper product, you could try a squirt of a general purpose lubricating and cleaning fluid, such as WD40. I've successfully used it to clean potentiometer contacts in the past but, if you try it, use only a very small amount, then operate the volume control (with the radio switched off) before leaving it for several hours to ensure that there's no liquid left inside the potentiometer. Don't turn the radio on (especially if it's mains-powered) if there's the slightest possibility that any fluid is left inside the potentiometer. (Proper switch cleaning fluid evaporates almost immediately but WD40 takes longer).
Chris