rncbc.org a.k.a. Rui Nuno Capela

You probably don't have the metronome setup done right. Adding to the confusion, qtractor has two metronome types or modes: audio or MIDI.

The audio metronome is setup on View/Options.../Audio; you have to supply two audio sample files (maybe any format you can find, wav, ogg, mp3, flac, aiff, etc.), one is for bar accent and the other for beats. Qtractor doesn't come with any by default, you have to choose your own metronome sounds :) Audio metronome sound is streamed to the default Master output bus unless you choose to have dedicated audio outputs for which you'll have to manually connect yourself.

The MIDI metronome is the one which is setup as default (View/Options.../MIDI) and that's probably what you see ticking in the mixer. However, to hear any sound you should route the default MIDI Master output to some synth or sampler, preferably a GM enabled one as the metronome notes are sent over the MIDI channel 10 (GM Drums & Percussion). You can also have it rendered through a DSSI, native VST or LV2 plugin inserted on the Master MIDI output bus. A plugin which loads a GM soundfont will please the effect just fine. I suggest fluidsynth-dssi, for example.

Cheers