I'm watching Channel 4 catch-up at present, and that is the only programme running - nothing else is open on my desktop computer - but every now and then I keep getting about 20 seconds of music, I think that it must be an advert by the sound of it, but where is it coming from and how do I stop it? I don't think that it is from any of the adverts displayed on the channel 4 page, and no adverts have come up under the ch 4 page - it's a mystery to me, as well as being annoying! Any sensible suggestions would be appreciated.