Is there something wrong with my instrument?

Hi! I've had slight problems with my flute. For some reason, when I play and F or a G, there's a small buzz sound. For instance, if I switch from D to F, I can hear a little buzzing sound. I'm not sure if anything is wrong with my flute. The same thing happened about a month ago but ceased. Now it seems to have come back again. Help please? If I do have to repair it, about how much are the costs? Does my flute need to be repaired? The problem is very slight and hardly audible, though.