Don't know if you'd consider this a bug but - Maetronome does not produce any sound when the phone is on silent. I thought that generally apps which you rely on for their ability to produce sound would do so even when the phone is on a silent profile - for example the media player still plays sound when the phone is set to silent. I don't think a phone's "silent" profile is the same as "mute" - its purpose is to prevent random unexpected sounds from phone calls and text messages.