XPS 8960, ticking in standby

I have a 1 year old XPS 8960. When I place it into standby and then return (e.g. the next morning), there is occasionally a ~1hz ticking noise coming from near the power button. It's still in standby, nothing appears to be running, apart from the ticker. Is this a fault, or is the PC trying to tell me something (like, firmware update needed or)? The ticking stops when the computer is woken up.