Noise with Hi-Res Lossless Music via airplay to Network Streamer

I have been using a Cambridge Audio MXN10 Streamer in combination with Apple Music (I know it is not high resolution) for some weeks, whenever I switch to „highres lossless“, I hear noises like from a dusty record on a  record player. I listen with a Beyerdynamic 990 headphone via a small Yamaha receiver, both, the MXN10 and the iPad (used for Apple play) have fixed IPs and certainly are connected to the same WiFi network. The MXN10 is connected to the receiver via analogue Cinch cable.

Any ideas where this noise comes from?