I have bumped out the size of a return into a closet to allow more air flow in my house and added shelves around it for added storage in one room. I know sometimes it is easier and can actually add to a room to put or enlarge a return and make a area for photos or small shelves in the corners of it.

I have seen laundry chutes sealed and converted into hvac supplies and returns and also seen them added into newer homes with part chute and part ducting right in the middle of the house even. It sounded like an awful idea but afterwards really looked nice.

I can't remember how much size you need per cfm at the top of my head but before I did anything else make sure what you have is not restricted from floor to floor. I took my cell phone and shot pictures down towards the basement and only had one 3" hole per return bay with a nice big 7x14 vent causing horrible return airflow.

The current return is too small. The question is what does the duct look like between the register and the furnace?S Sharp 90 degree angles cause air flow disturbance and noise. You want to eliminate these as much as possible.

There is nothing wrong with a floor return. It takes up floor space where you may want to put furniture. A return high on the wall makes it easier.

What is he adding on a 4 inch wide return in the floor? The narrow opening may still cause noise problems.

What size furnace and AC do you have? Usually the AC needs more air flow then the furnace, but you could have an over sized furnace which is starving for air.