Heat Pumps and Electric Heating - Heat pump sounds like cappuccino maker

I have a 7 year old York heat pump. This winter it started making noise when the heat comes on. It appears to be coming from the pressurized line between the outside and inside units. The noise starts a few seconds after the blower starts and continues for a few minutes. The best I can describe it is that it sounds like the banging & rattling a cappucinno maker makes when it is heating steam. I've had a technician here twice. He said it was low on coolant because the cap wasn't tight but said there was nothing he could do about the noise except replace the heat pump. Any ideas?

i have no idea what a cappucinno machine sounds like, but any noise other than a hum from a heatpump should cause a concern. o.k. here comes some questions, how old is the compete system (airhandler ((what make)), the home,
where are you located, first time this has happened, only in the winter months,
is the noise coming from the inside or outside units, and finally, other than the noise, does the system perform like it should (comes on when it is supposed to and shuts off when temp is made)? let us know, we are here to help.

barry

The system was installed when the house was built in 1998. It is a York. We are in coastal South Carolina. I didn't hear the noise until this past Fall. It never made this noise with the AC but it might when it gets warm. It does not produce hot air like it used to but does warm the house eventually and turns off. I know a heat pump never blows hot air but it seems a bit cooler than last year.

Now this is the strange part. I don't hear the noise at the inside unit in the attic or at the outside unit. But I do hear the noise in the wall from inside the house about 5 feet from where the outside unit is located.

The noise is similar to the steam noises that come from a coffee maker.

Could the freon level be low?