Trend bound to be picked up by radio (4)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

Homophone (to be picked up by radio = heard, although I think either “picked up” or “by radio” would be enough) of TIED (bound). As in Shakespeare’s Julius Caesar : “There is a tide in the affairs of men . . .” = a general direction at a particular time.