DEAR SAM: We recently purchased a new house, the exterior of which is antiqued white brick. There is a mud-stain all around the house covering the lower 18 inches. The builder told me that nothing can remove the stain. Obviously, it is quite unsightly. What do you suggest?

Answer: Your roof gutters apparently over-flowed and the water splashed around the foundation. [WORD ILLEGIBLE] around the base of the house could have prevented this, as could much. Does your house have a warranty under which the builder is liable for the cleaning? Has he tried household detergents, such as Savogran Dirt-Off or Mr. Clean, mixed in warm water and applied with a bristle-brush?

If these don't work, Prosoco Co. makes a liquid cleaner that is $4 a quart. A masonary supply dealer should have it or you may write to Prosoco, 1040 Chelsea St., Trafficway, Kansas 66104.

DEAR SAM: Our new house will be finished this spring. The heating and cooling system consists of two units of two-ton heat pumps for a 3,900-square-foot house. Since one unit will be located in the attic, what precautions can be taken to avoid noise and vibration?With blown-in insulation, 12 inches thick, for the attic floor, will Dennycell II sheet insulation be advisable for the attic rafters and gables? How can we soundproof the powder room plumbing, which is located in one wall of the living room? We have been advised that the house should have "perimeter insulation" with styrofoam.

ANSWER: Using two heat pump units, with one installed in the attic, I would recommend fiber glass ducts, one inch thick, in four-inch diameter or larger.

Although you have an excellent R-factor with 12 inches, be sure that a vapor barrier is installed beneath it. Also, ventilation from gable louvres or the ridge vent of the roof should not be limited or precluded in all seasons.

You can soundproof the new PVC drain pipes with "sliced" and metal-banded. For several pipes, a "box" of the studded wall could be insulated with thick bats stapled to the studs.

Perimeter insulation is used primarily in houses without basements or where the basement floor is within the frost line. Rigid styrofoam insulation in 2x8 foot lengths, two inches thick, is installed along the perimeter of the foundation extending two feet into the basement.

Samuel Fishlyn's address is Box 62, Newton Centre, Mass. 02159.