I would beg to differ with the first respondent, because there is surely a difference in TONE between the two meanings. While they explicitly appear to state the same meaning - and the first respondent is correct that "gotta be" is the same as "got to be" which does mean "must be", these small semantic steps do not lead in the direction of meaning, but rather away from meaning, which may be part of the intended purpose of the language. Therefore, "there's gotta be" suggests an urgency or more famililar or, frankly, lower social-economic class, than "there must be"... which, and it is only a wild guess, the author of the quote in question was trying to implicitly communicate as if through the subtext of the slang used. Great question! Thanks for asking it. Max

They both mean the same thing. "There's gotta be something wrong with him" is just another way of saying "There's got to be something wrong for him" which means the same thing as "There must be something wrong with him."