Hey Holly,

It could just be the action is too low (or the higher frets are uneven) and the string is buzzing against the frets. If you just hold down that single note on the B string with one finger, do you get the buzz?

This could just be an issue of neck / truss rod adjustment, or a fret could be too high. (Or a fret below it could be dented).

Try using just one finger, and go play every note up the B string, from the 1st fret, all the way up and see if you hear any buzzing or notes getting choked. If so it's not your technique, and it just needs an adjustment from a music store or tech.

By the way, this is a totally normal phenomenon if your action is too low (we have this often here when there are seasonal changes), and it could be a simple tweak of the bridge.

-Carl.