No Metronome sound exported

Try to record .wav file for ear training but failed to export the metronome sound with metronome turmed on:
1) in factory default setting turn on Metronome , also Concert pitch, and play the music score. The Metronome sound were heard clearly.
2) Export to a .wav file.
3) play the .wav created in step 2) but can not hear metronome sound.