4 year old keeps what asking “what did you say”

So my 4 year old son has never had a health issue but for the past two or three months he keeps asking “what did you say?”. I can’t tell if he’s having a hard time hearing or if something is wrong cognitively speaking? I’m sorry, I’m not trying to sound ignorant or insensitive, I just don’t know if that’s a thing. I try to Google it and I can’t figure it out. I’ve been writing it off as he’s just repeating what I say, because I say that a lot to his father who mumbles often 🙄. Or maybe he says it because he doesn’t understand what I’m saying and wants me to explain it. When I whisper, he hears me, and I don’t really see any other signs of him being hard of hearing. I don’t know if it’s something that’s common or if it’s something I should worry about.

UPDATE

thank you everyone for responding! I’m glad I’m just being paranoid and crazy.