Idiom
sound someone outsound (someone) out
to carefully discover what someone thinks or knows.I thought it might be good to sound him out about having you come to work for us.His policy was to sound out top business leaders before making any new economic proposals.
Usage notes: used to describe a way of asking about someone's opinions without upsetting or angering them
Etymology: based on the idea of sounding out a word you do not know by carefully pronouncing each part of it