I had a new Amer. Std. Heritage 15 2.5T heat pump with a TAM 7 air handler installed in the summer and it was super quiet. I turned the heat on for the first time about a week ago and now when it runs in heat mode I hear metallic sound that seems to be resonating through the line set. The air handler is in the basement and I can really hear it down there. It definitely is not coming from the TAM 7 air handler. The heat pump is working fine. I just want to make sure that is normal operation for this brand. My old York heat pump sounded the same in heat or cool mode. Thanks for all that reply!