Heat Pumps and Electric Heating - What in the world could this sound be ?

I have a goodman heat pump. It's the ONLY heat we have and we know nothing about it. We just moved into this house 6 months ago and haven't had any problems with it at all. The previous owners had it installed approximately 2 years ago. Our problem is since it has been snowing and cold we hear a rattling/thumping noise kind of like something is down in the fan. Could this just be ice ? We don't hear the noise all of the time. When you walk up to it when it's making that noise you can actually feel ice hitting you. The heat is working fine. I can hear it defrosting also. Just not sure if there is still ice in there causing the noise. Any help would be Greatly Appreciated !!

Reminds me of a call from my Mom a few years ago.

Down in Myrtie Beach they had had an ice storm. All the heat pumps had an ice crust, made noise and spit bits of ice.

I told her to turn on the A/C for 10 - 15 minutes and melt the ice. Let it rest for 5 minutes and turn the heat back on.

Word traveled fast and all the retirees found other things to worry about.

Next time you hear this shut down the unit, go outside and look inside to see if you can see anything loose that might be banging around. If you are handy shutdown the outdoor units power, open the maintenance panel and look inside. You could have a loose wire, insulation, or tape that ice is forming on and blowing around.

In defrost mode the outdoor fan should not be running.