Thanks to everyone who provided advice! Much appreciated.
To answer some specific queries above:
@ghdprentice: the WiFi extender was an excellent suggestion. I did purchase one and, indeed, it appears the static sound isn't occurring quite as often as before but it doesn't completely eliminate the issue, sadly.
@kiwiscott: I did change the output signal of the streamer to CD quality and tested it. Then moved to the next output quality and tested again. No change. But the local file comment is a good one, so thank you! Local (FLAC) music files connected to Roon on the network don't appear to show this issue, it's only Qobuz (via Roon) and Apple Music (via Airplay) that are problematic, so it's internet related in some way.
@kiwiscott: Yes, everything is plugged into the same outlet.
@steakster: Yes, definitely rebooted the modem/router many times! No change.
Also, changing the stock 18V power adapter for a more decent model doesn't change anything either. I'm largely out of ideas now...but perhaps @yage is correct - I'll contact the local distributor and see if the item can be inspected/replaced as it might be either a defective unit or the design itself is flawed (hopefully not).