Yes I'm buying a 1000 ft 2bedrm house and the people who owned it before had a new coleman ac and heater and during the summer everything fine and dandy but now that I'm running the heater every so often after the heater runs it makes a nosie like an old dying hissing machine is this normal ? Cause if not have not signed all the papers and well need them to have it checked out before signin

If it is a heat pump system it is possible the noise is somewhat common BUT I would have it checked by a professional on site just to make sure. Upon shutoff refrigerant movement can make that type of noise especially with a bleed style expansion valve..