Couple of questions:
1) is your receiver a FrSky or a Flysky? I do not believe that latter is compatible with FrSky.
2) Is your sound system integrated with your motor controls, ie, ESC's? If so, you might consider disconnecting the sound system and then trying your radio system as stand alone. If it works then, then your sound system connections are an issue.
3) I am running a Tandem XE, but admittedly I have not tried using a Tandem receiver. That said, make sure that you settings in the transmitter are correct, ie, which antenna you are using, internal/external module, if using Tandem that you have set the appropriate output level(watts) ect, ect.In the worst case scenario, use the KISS principal. Start from scratch by hooking up just the radio with basic controls, rudder, throttle. Add one additional layer at a time. If the condition shows up again, it will be because of the last layer that you added.
Good Luck.