You still got a chance to be some air trapped in. It happened to me before the only way to get the air out was using the vacuum bleeder, if you are close to my garage I can do it for you. If not try to find a decent garage locally have this equipment. (Of course it's can be something else, but really sounds like air in the heater matrix.) Also have you got this noise every time ? Did you run the A/C when it's do the noise ?