Janice 26,
There are many examples of closets in the photo gallery and many posts discussing the issues and solutions. Heat will rise up in the closet to the motor, right where you don't want it. If you build a "chimney" on a side of the closet that is open at the top and vented out thru the wall at the bottom then the air from the filters will sweep the hot air down the chimney and out of the closet. Several have used baffles to reduce the sound level traveling down the chimney. Also, a number have used rock wool insulation to line the closet to reduce noise. I think that is a good choice since it is fire resistant and inexpensive. Good luck,
bababrown