I would bring this up at my next doc appt...or call to find out if you should come in sooner. I can't imagine what sort of info this board would be able to give you that could cause undue concern, even though it would be well-meaning.
Vive:Keep an eye on your babies responses to other sounds... Particularly ones that occur behind them such that they aren't getting visual cues that a sound should happen. And yeah I'd mention it to the doctor next time you see them.
All this. What can be concerning is that babies with a hearing loss will start cooing at the same developmental time as typical babies, but they will stop because they are not receiving the auditory feedback that would lead them to continue.
Keep an eye on LO and bring it up to pedi when you get a chance.