Sudden audio problems

Since a few days I suddenly have the problem that all movies have problems with the audio. The sound is in the background and only when spoken words or singing is heard. So silent moments remain completely silent. Nearly all movies are .MKV and have AAC and AC3 tracks. The 2 settings in Infuse are both on disabled.

Nothing has changed in the setup. The aTV is connected to the TV thru a HDMI cable. There is no separate audio.The setup has been unchanged for years.

How can this be caused?