Yes, ‘were your ears ringing’ is an idiom. This phrase is often used to ask someone if they were aware that they were being talked about, usually in a context where the conversation might have caused their ears to ‘ring’ metaphorically. The idea is that if someone is talking about you, you might somehow sense it, as if your ears were physically reacting to the mention of your name. It’s a playful or humorous way to suggest that the person might have felt a subconscious awareness of being discussed.