Have a combo oven/microwave mounted in the wall, GE model JTP55. Everything works but microwave doesnt heat. Also seems to be making an unusual buzzing noise while trying to heat. Would like to test parts but they are in the back and hard to access. Does the microwave need to be removed from the cavity in the wall to test? If so how hard is it to remove and can the microwave be removed separately from the oven? Thanks!