I have a 1998 GMC Sonoma SLS with a 4.3 l V6 Vortec.
It used to purr, now it growls, sounds like a small diesel engine. Vibration can be felt (mostly in the dead pedal) and also vibrates/growls in park and neutral.
Just came back from usual oil change, but has never sounded like that before, usually a nice quiet motor. Also significant vibration at 90 kph, smoothing somewhat at 100 and up..Any ideas?