I have a client who is complaining about the knots in the paneling inside their mobil home. The knots have darkened noticably in the last six months and the knots are also etching or shrinking. Does anybody know what may be the cause of this? Is it chemical, biological, or just age? The home was manufactured in 1982. They recently moved it 8 miles from Tacoma to Spanaway in Washington. They have a heat pump and a pellet stove for heat.