Listening to it longer, it is mostly Hiss --> Tick --> Silence --> Hiss (but on a variable time interval between Ticks and how long the Silence is).

Also - I can rule out the source (into the AVR) as it happens across all sources.

HT:M80,VP150,QS8,EP500 Outside:4xM3 Office:AudioBytes, Rumpus: M60,VP150,M22 Portable:2 x Airs