2003 Silverado 1500 Sportside 4WD Z71. During light acceleration, or anytime that the engine would be under load. . . vehicle travelling around 40 or so MPH . . ..hear a light growling kinda sound, and feel a light vibration. I think it is probably Universal joints. . . .but hate to think so since Universal Joints and Driveshaft were replaced around 35K miles and I have about 69K on it now.