I just recently bought a 89 blazer. everything was stock when i got it 31's and no lift the 4x4 worked fine with no sounds or any problems. i just put a procomp genuine 4" susp lift and 35's on it. now the front end rattles/clunks when i gas it from a stop. it only makes the noise when i am stoped or driving les than 5 mph. there is no slack in the drive shaft and i have checked and rechecked all new bolts and hardware i installed. any ideas what it might be?  

ive just read about lifting mistakes often made last night...and im in the same boat...havnt lifted my jeep yet cause i have to change some stuff,but people dont look at the big pic when lifting rigs...all of your ball joints, tierods, relay rods pitman arms dont get change and have thousands of miles on them and are worn out...chances are one of these componants have a hell of a lot of added strees from the lift and now your noticing the problems now instead of before you lifted it.check everything now and if i were you id change everything so you have good strong parts to go along with your lift!...im gonna have to do that first before i lift my jeep cause its pretty ratty looking!   good luck!  

You may be dealing with a bad bearing in the T-case, front pinion, or it could be as simple as a U-joint. Try removing the front shaft and see if the vib disappears then work your way from front to back. Best of luck.  

I will agree with both of them.  Lift and larger tires will magnify a problem that you hardly noticed before.  

iF it were the u-joints wouldn't i notice slop in the shaft? how easy is it to replace bearings or pinion gears. also looking into getting 4.10 or 4.11 gears whats the scoop on new gears and the best place to get them.  

U-joints can make noise even with very little slop.

For the 35" tires you now have, I would recomend 4.88 gears for better power, fuel economy, and transmission life.  The 700R4 trans has a .7 over drive and with 35" tires and 4.88 gears at 60 MPH the engine would be at about 1968 RPM.  The actual original tire size was 235/75R15 ( 28.9" dia. ).  With 3.73 gears and those 28.9" tires the RPM was 1821 at 60 MPH which is actually on the low side for RPM.