Rhythm track won’t play thru audio interface

Greetings,
I’m using Audacity 2.4.2 on a Mac running OS 10.13.6.
I am able to generate a “rhythm track“ (a.k.a. “click track“) OK, but;
When I play this back through headphones which are plugged into my audio interface, the Metronome clicks are almost completely in audible. Likewise, if I start recording a second track, trying to follow the rhythm track, I still can’t hear it. However, once that second track is recorded, in the playback I can hear both the rhythm track, full y audible, along with the 2nd. After that, while recording any further tracks, the rhythm track is fully audible, as long as BOTH it and that 2nd track are not muted. If I mute that 2nd track, the rhythm track again becomes inaudible. It’s not that the metronome clicks have somehow got into the 2nd track: If I mute the rhythm track it disappears, even though I leave the 2nd track at full volume.
(The rhythm track plays fine thru the computer’s built-in audio, but of course I don’t want that playing aloud while and getting picked up my the mic while I’m recording a track.)
This makes no sense to me.
The audio interface in question is an iRig PRE HD, an otherwise excellent piece of equipment.
Any ideas how/why this is happening and how to make it work correctly?

Kurt B.

It sounds like there’s some kind of audio “enhancement” effect being applied on playback that is suppressing the clicks.