Q. Our forced air oil-fired heating system is 35 years old, and over the years it has emitted a shrill howl in B flat, on and off. Sometimes it cycles three or four times a day. It tends to howl when the oil burner is off, so it must be in the blower and in the ducts. Have you heard of such a thing?

LEE ENGLER AND INGE THORN ENGLER, WESTON Lee Engler and Inge