I have a very weird problem with my ctk6000 keyboard. The keyboard plays fine fine for 10 minutes but after that its volume starts decreasing gradually until it becomes inaudible. Everything else keeps working fine like the screen. Now when I shut off my keyboard for another 15 minutes and power on the keyboard, it plays good for another 10 minutes but again the volume starts diminishing gradually. Anybody else has faced the same problem? Is it the problem with my adaptor or the keyboard?