It may need a new float valve or washer if available. If the washer is old (modern float valves sometimes only last a few years) or the valve has dirt in it they can make all sorts of strange sounds. Hope this is of some help.
Andy, January 2009
it could be your water level is to low
clare, January 2009
edit
I can answer this question...
when i flush the toilet there is a noise from the water pipes?
