This receiver may lose sound or the mute setting may be activated if the Consumer Electronic Control (CEC) setting on one of the devices is set to on. The CEC feature may be interfering with the HDMI control function. Simply disable the CEC control of the TV and turn off HDMI control on the Sony device.
NOTE: The CEC feature on Sony products is labeled BRAVIA Sync. However this feature may be labeled or called something different on other manufacturer's products. Refer to the operations manual of the device itself for additional information.