I'm aware that some receivers "click" during commercial breaks as the sound changes from 5.1 during the program to stereo during the commercial. A clicking during music playback as you describe is not right.

I am curious if the clicking will go away when the setting is 4 Ohms. Can you try that?

I'm also curious what source you are using for music.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated