The door seal typically will have a maximum radiated signal of under 5mW of power, 5cm from the door ( the pass fail limit of a microwave leakage detector) so, as your typical bluetooth transmitter will have a power output that is almost that, the microwave will win with it's noisy 50/60HZ modulated broadband noise whenever the receiver is getting a larger signal from this leakage than from the transmitter. Microwave passes it's level ,but it is just that the allowed leakage is more than the bluetooth transmitter power.