4wd/Auto noise

buickwagon

SM 2017
Full Member
The snow has finally arrived and so I have started playing with the 4WD options.

There is a very noticeable hum under load in Auto, similar to tire noise. It is first detectable around 20kph (~10mph) and rises in pitch with vehicle speed. It rises in volume up to about 60kph (~40mph) and decreases in volume beyond 80kph (~50mph). It virtually disappears completely when coasting under very light throttle, but returns just as loud when engine-braking.

There is a similar hum in 4WD high, but slightly deeper in pitch and much quieter at lower speeds, ie 40 or 50 kph. The pitch of this noise also rises with vehicle speed. The volume is similar to the noise in Auto at 80kph and continues to increase to freeway speed -- 100 kph (65mph) and beyond.

Is this normal or should I be concerned? I've never had one of these automatic 4WD systems before. Some preliminary research on the internet suggests that this may be normal for a chain in the transfer case, but it is somewhat disconcerting.
 

AirJunky

Full Member
Stop driving the truck. Either the transfer case or front diff is about to grenade. Get them checked immediately
 

redheadedrod

SM 2017
PM 2015
Full Member
Sounds normal to me. If it is low like tire noise then it is just your 4wd system working. If it is louder than that then you may have something going on. You can always have it checked out to make sure your transfer case isn't self destructing too. The 2003-2006 transfer case has a factory defect that causes the case to self destruct if not dealt with. This can show its self as a noise as the fluid slowly "leaks" out. Normally pops a hole in the top of the case which means you don't see it leak out since it doesn't make a puddle under the truck when parked.
 

malbrecht1

SM 2017
Full Member
I had a similar noise with my 03 Avy, but it turned out my front differential fluid was low. I filled it up, and now I can barely hear it.
 

buickwagon

SM 2017
Full Member
Ok, I got under there and pulled the fill plug. Tried to stuff one of my fat sausages in there to find the level. Things were wet with oil but couldn't feel a level. I added 600mL (about 1/2 quart) of 75w-90 synthetic, which brought it up to the bottom of the fill hole. So I guess any noise I hear is just normal for this truck.

Thanks all.
 
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