I am having exactly the same problem. The sounds you get from pushing "OK" on the remote plays every 20 seconds while using Tunein.
I'm noticing it as well, it's the menu clicks, like you're pressing your remote. I wonder if they do that to channels that don't have ads until you pay for premium...
Yes, in the TuneIn app, playing any station, you hear the basic button-press sound every 20 seconds exactly. this is on a TCL-Roku television.
Same problem, all channels, local or international.