When I was young I had a lot of ear infections...my eardrum burst once too and I remember having to get my ears suctioned out when I was little. I had tubes and that helped out a lot...I don't know if I had hearing issues or not...but I think
that's why I had them suctioned.
But I second that the ear infections and loud vehicles may have something to do with it if there is something wrong. And as JDI said...if it does come down to something, that this is a good age because kids are great adapters and it'll be easier to "get used" to it.