Bluetooth problem on Teac NT-505

Hi, I have a Teac NT-505. When I use it in bluetooth mode with my Sony Xperia XZ2 smartphone, sometimes I hear interference while listening. I don't understand how it's possible, since the smartphone is fully functional, the 2.4Ghz channel wifi is disabled, the Teac software updated to V1.21 and NETWORK Firmware Ver11.1e. Can anyone who has an NT-505 like me help me? Thank you