DM-40D speakers bluetooth flikkering

We own the DM-40D speakers for two years now. 
Suddenly we have the problem that the bluetooth light is flikkering really fast. Faster than when he's looking for a device. It doesn't stop flikkering and can't connect as well. 
We have already tried turning the speakers off and on. We also tried unplugging them from the socket. Nothing works. Does anyone know a solution?