As I don't think I chimed in on the other thread:

Never never never! Even if it is not loud its still enough of a distraction to be dangerous and you need to be alert when riding - on the road or on a trail. Unless you are accustomed to being deaf, your ears are an integral part of your alertness.

Personally I think joggers/walkers shouldn't even wear them if they are on a multi use trail - on your left, on your left, ON YOUR LEFT!!!..........