Im new, need help with tranny sound

Hey guys I just bought an 05 Stang GT yesterday, and as Ive been driving it, Ive noticed that if Im cruising and rev to around 4k rpms and shift, I hear a sort of clunking sound when I engage to the next gear..doesnt happen if Im driving it hard, just when im driving it in the mid rpm range and drop the clutch into the next geat. I know this is common on autos but mine is a 5spd manual transmission. Is this sound indicitave of a problem or is it normal? (This is also my first V8 RWD, so I dont know)

Thanks!

as a note, I have searched around and cant really figure it out...UCA or LCA bushings? would these be a problem even if my clunking only happens when I start or shift?