Heat pumps are loud. Any insulation around it may disrupt the air flow and burn out a compressor. One option might be to replace it with a quieter one or go to a new furnace/ac setup with a quiet scroll compressor. If you buy anything new, ask to see and hear one in service before buying.
Another option would be to move it to another area of the house away from the deck such as on the side or in front and plant a bush or two by it.
Most people in the country are shoveling snow off their decks, where are you at?