Yesterday I bought a second handed CODE 50. There were no problems at the buyer's house, but when I tried to make a bluetooth connection at home, it failed. I restored the factory settings and updated the firmware to version 1.44. I still can't make a bluetooth connection (iPhone 6s, iPhone X, iPad, MacBook Pro, all with the most recent iOS and MacOS versions) and now also the amplifier loudly knocks every 3 sec. I tried all suggested solution, but still no bluetooth connection. And the knocking sound is really annoying! How can I solve these problems?