Has anyone insulated to cut down on furnace noise?

Sound deadening material

This material is self sticking. It moulds around places.

I have this on both of my gas furnaces. Often the air intakes inside the rv are very large and directly in front of the intake fans. If you can place something a few inches in front of the noise and let the air go around the sides the noise will be much lower. In some cases you can block off a large portion of the intake.

This material is close to 1/8 inch thick. When warmed to room temp or higher it is very easy to use.

I have had my furnaces covered for many years. There has been several write up on a couple of forums so doing a google search may find them.

Here is one example