Front Clunking noise when in 4WD
 

I have an 03 2 door Blazer. When in 2WD everything is fine. When pressing 4WD it engages properly and drives normally. At random times, however, I hear a clunking noise from the front that sounds like a hammer hitting a solid piece of metal. There is no pattern to this as I can drive several minutes without any sounds and then it can do it a couple of times in a minute. Switching back the 2WD and all is fine. Any ideas as to what should be looked at?

Does the clunk sound/ Feel like it is right below your feet? Check your transfer case fluid level. I Had the same symptoms when I first bought my blazer and my transfer case fluid was Veeery low.

Feels like it is a little more forward than that. I have the truck at my mechanic today and he does not see anything wrong with u joints, fluid levels etc, but noticed that one of the motor mounts is totally broken. He tells me the engine torques more when in 4WD and that may be causing what I am hearing, hopefully that is the case. Repair will be completed tomorrow. Thanks for the reply.

Well I got the truck back from my mechanic with the motor mounts and transmission mount replaced and I still have the same clunk/banging noise in 4WD only. He wants me to bring it back next week and bring it to a tranny place to examine the transfer case and transmission. Any ideas would be appreciated. Thanks

...besides a new mechanic? sorry couldn't resist

edit - I guess that wasn't very helpful - are you sure it isn't happening when you turn the wheel one direction or another and give it throttle? How about on uneven surfaces or rough roads? Where does if feel like it's coming from?

Going straight, does not seem to be related to steeping on the gas or not as it has made the sound under acceleration or letting up on the gas. Road surface is smooth. It does not appear to be anything loose. I would estimate that the sound is coming from a location forward of the transmission. As I had described earlier it does not make this sound all the time. Motor mounts were bad so it seemed like an obvious place to start before doing anything else.

Look at the Drivers side Wheel Hub, I had similar symptoms aswell a second time and it turned out to be my Wheel Hub, a much cheaper replacement than what my mechanic originally suspected when we replaced my transfer case....So once again, Check your wheel Hubs, My noises started at around 90KM/h and stopped around 100km/h then the speed range progressively became wider.