I used to rely just on listening for engine problems. A veteran mechanic let me use his stethoscope and pinpointed an issue I'd have missed. Do you guys always use tools for noise diagnosis?
My buddy had a weird ticking in his truck for months. He kept thinking it was just valve noise until he borrowed a mechanic's stethoscope. Turned out to be a loose heat shield rattling against the exhaust manifold. He would've never found that by ear alone.