Sounds like you may need 2 new 'Nggg, Nggg's' they get worn after a while, Halfords sell them in little red tins but be careful when you open them because they jump out and go Nggg Nggg straight up your noise!
Thanks mark for your informed reply... actually halfords have changed the colour of their own brand ones to blue with red stripes, but aparently these don't last as long, and can cause noise bleeds.
@Matt: Perhaps you could tell us if you can feel any abnormal vibrations in the car, your driving style, the milage on the vehicle (or distance traveled since new), and any other info you may feel important.