02-09 Vortec 4.2L I-6 Engine and Drivetrain
2003 TB 4.2L I6, 190K miles. At idle, using a stethoscope, my deep rattling noise is loudest from the timing chain cover. All accessories and idlers have their unique "normal" sounds, each with a hint of the same sound in the background. It's also quite audible in the engine compartment...