Acoustic Guitar problem with string?

HI, i got my first acoustic guitar like yesterday and I got an electric tuner. So i tuned all the strings and they are all in tune. All sound good except the B ? they all sound full and nice but when i strum across the b string it like vibrates and sounds well awful? its in tune but I just don't know what it is? Anyone got any ideas and how to fiz this vibrating noise coming from my guitar string :P ahah x thanks !!