I have a 03 suburban 4wd and it has a growling noise that varies with speed and also increases when 4high is engaged. I put the car on stands and ran it in the air but was unable to duplicate the problem. Every thing runs quiet,wheel bearings, front diff.,drive shafts ect... With a stethoscope on the transfere case I can hear some whirring. I noticed that the front drive shaft turns both in 2wd and in 4wd. Is this normal operation? The service 4wd indicator goes on intermittently.

SOURCE: '95 tahoe making noise when accelerating; sounds

no it should not spin when is in 2wd thanks

SOURCE: front diff growl in 2wd

This would be a failing bearing in the differential. More specificly, I would suspect the pinion bearing. The differential will need to be disassembled and all (4) bearings and bearing races inspected for wear/ pitting.

SOURCE: 2000 suburban 4wd-drive train vibration

Have you had all the wheels balanced? Have you checked for a bent axle?

SOURCE: 2002 Chevy 4wd

maby im wrong but if you rev up and only rear wheels spin that means that it might be 4 wheel drive but not constant 4 wheel drive or diff lock system ,,,, ,, in 4 wheel drive all wheells will turn together but if pressure of slip is bad enough or torque high enough only 2 wheels will drive ,,, thats why diff lock locks wheels together in each axle to over come this ,,, all wheel drive like in landrover locks all 4 wheels together to ensure all wheels rotate to give best grip