What is the ruling on listening to the Adhan of the people of innovation while enjoying their voice?

It is forbidden for a Muslim to enjoy listening to bid'ah (innovation in religion), because it contradicts the obligation of enjoining what is right and forbidding what is wrong, even if it's only by the heart. Enjoyment is a sign of approval and contentment, whereas disliking it in one's heart is an individual obligation that cannot be waived. This involves hating the objectionable act and shunning its practitioners when one is unable to change it by hand or tongue.