Question about Philips Sonicare Series 3100 Doppelpack

Hello I bought the Philips Sonicare Series 3100 twin pack yesterday. According to the instruction manual, the handpiece emits two short beeps when placed on the charger to confirm that the handpiece has been correctly placed on the charger and is charging. In our case, however, both handpieces emit a beep every 31 seconds. That's really annoying when it beeps every half a minute. We had to remove the handpieces from the charger as it was impossible to sleep at night or concentrate on work during the day. Does anyone have a solution to this annoying problem? Otherwise there is just a warranty case.