Just wanted to share:
 

I was faced with the choice of renewing WiFi (deco M9) or another speaker. Because I decided to go for the latter, I was bought a Deco M5 as an extension. Surprisingly enough, now that the hk citation one is connected to it, no more creaking or popping sounds. Accidentally connected the speaker to the m9 again and immediately problems again. It's now set on the M5 (something the m9 can't do) and I'm Happy! 2nd hand M5 for 30 euros was the solution to years of irritation.