Heat Pump Noises - Got Problem or Normal?

[cold55]

I don't recall noticing this problem during the first one or two years but I notice it it now and it's gotten a bit annoying.

On my carrier greenspeed, one of my lineset that goes into the wall of the house into the crawlspace, near the heat pump is making a knocking noise (3 to 6 knocks) when the heat pump is defrosting . It sounds like it's from the suction tube line (vapor line?). This knock sounds like it's coming from the area where the line enters the house but then again, the sound may be transmitting from somewhere else. Normal?

Lastly, when the heat pump shuts down during normal heating cycle, it makes a loud stopping noise. It sounds like the switch has been turned off on a running compressor and it makes a sudden halt noise (best I can describe it).

Thanks again for you expertise! I wish more of you were out in my area!

[cold55]

I thought the knocking happened only at defrost but I can hear it during regular heating mode. I don't hear it all the time but it appears that the knocking starts when the Heat Pump is starting up. I don't hear it anywhere else either; just near the vicinity of the heat pump where the line enters the house.

What could be causing it?