Do you mean like single click/crack from time to time like very few seconds? (in extreme cases every second?). Yesterday I bought Scarlett 18i20 which is similar class of device and I have exactly the same issue. On Windows there’s no problem, on Linux I hear cracks on every machine I connect interface to (tried multiple PCs, laptops, multiple Linux distros).
Did you find any solution to your problem? It’d probably also solve it for me. Or did you maybe find some other high-channel-count interface that doesn’t suffer from this cracling?
I was planning to get Steinberg UR824 instead of Scarlett 18i20 to check if it works better but considering you have the same issue it’s probably not entirely interface-dependent. I believe it’s partially bound to number of channels since I have Steinberg UR12 and it doesn’t make such crackling noises (on the same machines). I also bumped into other channel-count dependent issues. For example when I load JACK in full 18+20 channels mode I can’t set it to any resolution above 48 kHz. In order to use interface in 192 or 96 kHz I need to force JACK to allocate only 10+10 local channels.
In such case I’ll get Behringer UMC1820 (since it costs pennies so I won’t cry if it’s not gonna work). I heard it’s super-duper Linux compatible (since it actually doesn’t have any OS X drivers at all afaik, it’s just fully class compliant) and I’ll try to just connect Scarlett over ADAT. My plan B at this point is to set up some Windows crapbox (eg Intel NUC) that will be hosting netJACK and