buzzer comes on when i engage torque on my 2003 jcb 3cx?

when i engage the torque on my 03 jcb 3cx the buzzer comes on the first min or so it's fine, then after that the buzzer comes on for a sec when you engage the torque after about 15 or 20 min of work the buzzer is on all the time only going off when you hit around 1500 revs or so, there is no drop in power still can push as much as ever just like to know is it just a senser or something that might do damage. the machine is a sitemaster plus with manule gear box, any ideas???