2007 Vauxhall Tigra warning beep

as soon as i drive off i get 5 'bleeps', if i go over a bump they stop until i hit another bump...sometimes they are not there at all...i suspect it will be down to a sensor and might also be linked to why the rook doe snot work (bloke i bought it off saw the roof going up and down at least 6 times before buying, first time he tried it did not work)
anyone had this problem before and give me some ideas?
tia
hoolio