This is water source heat pump in a condo unit. The HP made this noise for over an hour after a cooling cycle, going from louder to quieter before turning into more of a dripping noise. The HP is six years old. 

I had a tech come in, and it appears one of the water pipe connections, where the tube connects to the HP, was leaking and corroded. He suggested it was due to vibration. He also indicated that one of the copper pipes that feed off the water connection might have a hole in it from rubbing against the interior of the unit (due to the vibration), but couldn't confirm this. He left the water pipe unconnected and told me not to use it. I'm waiting for a quote on repair or replace. 

I also asked the original installers to look at it, and they reattached the water pipe and said it was fine. 

  
I just ran it for few minutes. Cooling was working fine, and the noise didn't happen again after I shut it off. 

So I'm left in a bit of quandary. My concern is a) is this a leak that will turn into a flooded apartment or b) is this something that will eventually break the unit if I keep running it? On the other hand, replacing the HP again after just six years is less than ideal. 

Heatpump gurgling/boiling noise?