[David Franklin]

Sounds suspiciously like a dialler - can't think of anything other than an analogue modem that would (a) sound like that, and (b) come from the back of the machine.

I'm not sure, but I think it unlikely downloading Firefox will do anything about whatever malware has already managed to install itself. I'd second the suggestion to download AdAware; the other thing worth trying is Spybot - each misses some things that the other catches.

Let us know how you get on - if you don't get anywhere, you may have to consider saving all essential data and doing a clean reinstall. But then I'm a bit like Ripley on this - "nuke it all from high orbit - it's the only way to be sure".

One other thing - if you can work it out, it would probably be helpful to know what website it's directing you to. This is often one of the ways of identifying exactly what piece of mischief has got onto your machine.

Best of luck...