We just moved into our 1990's ranch in southern california and had the A/C condenser/coils replaced (the furnace was in good condition). The unit works great but blower noise is a problem.

It's not the blower itself, it's the design of the house -- the furnace is situated in a small closet (raised above the air return) right inbetween our family room and master bedroom.

Is there anything I can do to reduce the amount of noise ... I thought about insulation on the walls of the furnace closet but not sure what kind is best to use in proximity to the furnace.

Also, would it be ok to install a filter over the air return grate?

Thanks for ideas/suggestions.