A dirty drip pan pad is often the true culprit in a smelly Singer Featherweight case. Read my November 2011 Tip of the Month for more information about Featherweight case odors.
Nova has the drip pan pads she sells custom made for her. They are made out of material as close to the original material that Singer used for the Featherweight drip pan pads as she could possibly find. They are far superior to the microfiber drip pan pads sold elsewhere.
Nova recommends that you change your drip pan pad every four years.