Weird pill shaped bump under kittens skin?

Well today I went and adopted two cute kittens from my local PetSmart. And about a few hours after I adopted them, I was petting Mystique (silly name,I know :lol3: ) and right above her shoulder blade, I felt a small pill shaped like bump under her skin. Worried, I checked Buddy for any bumps but didn't find anything. Mystique is a domestic medium haired cat. Should I take her to the vet? The people who ran the adoption thing gave us a free vet visit that's good for the next ten days... So should I take Mystique to the vet? Is this a serious problem? Thanks for ant help

It may be an id microchip? They are about the size of a piece of pencil lead.

But the vet visit is the best way to go....

I also think it's the microchip.  That's the general location of the insertion and it's about the shape of a grain of rice, only bigger.  I wouldn't take her to the vet for it, but the next time she's in, ask them to scan it to see if that's it.