Thanks to @Mirdarthos, in reply 3, who gave me the idea of the log-levels and how to restrict them, i started to investigate the level of those messages and it seems to be debug-level messages, because:
journalctl -u rtkit-daemon.service -p info
Successfully filtered them out, while the below still showed them:
journalctl -u rtkit-daemon.service -p debug
- systemd.exec.html#LogLevelMax=
- view-logs-using-journalctl-filter-journald/#9_Filter_logs_based_on_priority
I’m now using this as drop-in:
# /etc/systemd/system/rtkit-daemon.service.d/override.conf
[Service]
LogLevelMax=info
Lets see if they keep away now They are gone yay 
You can use different log-levels to make it even more silent…