What evidence is there to suggest the ghost is a projection of Hamlet’s feelings about his mother’s marriage to her brother-in-law?

There is little evidence to suggest the ghost is merely a projection of Hamlet's feelings. Marcellus and Bernardo have seen it more than once and Horatio has witnessed it as well. Hamlet never liked Claudius to begin with. We could tell Hamlet had mother issues even before he witnesses the ghost. Hamlet thought that Claudius was a nasty guy but not within the context that the ghost tells him.