That's OK. Loudness requires Internal Volume, so I wouldn't be here with this query if that weren't already set. I can see Loudness in the Audio Path when the volume slider is anywhere from 99% down. I have the systems calibrated to the reference level etc. etc. That's the basic stuff.
IMO the problem is not with any of my DACs as I observe consistent starting clicks with 4 different installs of MC on different hardware with different DACs although the loud "crack" is only a problem with one set-up that has an 18i20 Gen 2. I have two 18i20 Gen 2s and they operate consistently on the system that issues a loud crack part way through play with Loudness activated. Common factor there is a Lenovo PC that "could" be a factor, but I doubt it because it runs so well with Loudness off.
The little click on playback start is of no concern of itself. It is so minor that one might not even hear it. That's why I suggested earbuds to test it, but it is certainly there as a random artefact. You might have to stop and start play a few times to get it. It is quite audible on only one of my better active speaker set-ups, but on the PC at my desk it's innocuous unless I use earbuds and I suspect that others simply wouldn't be hearing it. I have aged ears and can hear it easily. It's similar in nature to the click in the files of PCM tracks converted with early software from SACD DSD extractions. I only raise it because I thought it might be related to the more serious loud and frightening crack that can come later in a track with Loudness on - that's a rarity though and I wouldn't expect others to observe it because they won't have that particular combination of gear.
I suspect that it is something that MC is doing "glitchy" with its Loudness implementation because it seems to be happening internally. Again and I keep saying it - the issue is ONLY evident with Loudness activated - which seems logically to exclude my settings and hardware from fault. With Loudness deactivated MC is extremely sophisticated and runs perfectly on all 4 of my systems. I would say I'm a reasonably advanced MC user with numerous zones, zone switching rules, EQ tuned to + and - 0.7dB from quasi-anechoic near-field REW measurements using Parametric EQ in DSP Studio etc. etc. I use JRemote on both Apple and Android to control the servers at fixed IP addresses etc etc. BTW "App follows Zones" in Android JRemote is bugged as it only follows a zone switch from the server once and then get's stuck in that zone for good. The Apple version is fine though.
Anyway I am not here to debate it. I have brought it to JRiver's attention and they can investigate it if they like. I'm 99% certain it's a coding error somewhere. End of rant. I'll just turn it off and use my own less-sophisticated 2-dial analogue loudness compensator circuit instead and maybe look at the updates here from time to time to see if it has been addressed.