While your up there...
Get yourself a can of compressed air... you know... the type used for cleaning computer keyboards, etc. Then use it to blow out the sensor area... it's a gap between the plastic top and the (probably) metal base. In the worst case scenario of not having a can of compressed air, use you vacuum cleaner (Oh, a Hoover in the U.K., no?) and using the crevice attachment, go around it.
Dust, bugs, small pets and other undesirables can get into this area and cause false beepings quite often...