Picture this rig. Left side is 1 lb. coffee can with 4 inch speaker mounted to bottom of coffee can to be directional with a bracket on side of can to C- clamp mounted speaker in can to vibrate surfaces if we cannot set can on paper to vibrate flat surfaces and protect finishes. About 12 feet of speaker cord goes to adjustable oscillator on right with enough amplifier to drive the 4 inch speaker.
Loose screws, bolts, and objects have natural frequencies. Car shut off and quiet. Roll window up and clamp speaker on to rattle door. Start at low frequency and SLOWLY increase while listening and feeling to detect rattles or vibrating objects. Most noise is dashboard so open glove compartment or C- clamp to bottom dash and run frequency range. Place on floor of car trunk, paper to protect fender and vibrate them. For best results do not hold speaker can in hand as this dampens frequency range.
