I just recieved a new yamaha Acoustalon YM2400 marimba, but some of the keys make an odd clicking noise when hit. I think the bars are defective, because the same marimba is at my school, an there is no clicking noise. I'm also thinking that it could be the mallets (Innovative Percussion Jim Cassella Medimum) What should I do?

well it could be a number of things

first of all, is it on both keyboards??
check the height of accidentals keyboard, sometimes it is too low and will click against the lower keyboard.

Second, it might be the resonator support bars..maybe try some felt around the edges

or you might have defective bars

Scott