Ok, 97 Jeep tj w/ stock 4cly & np231. Dana 35 w/ 4:10. Mods 3" black diamond lift, Detroit truetrack Locker, 35"x12.50x15.
Originally when I installed the lift w/ 31x10.50.15 I had a slight vibration & Noise. I tried the transfercase drop kit that came with lift but vibe was worse. I rebuilt the front driveline Which fixed the vibe, & replaced muffler which fixed noise.
I've drove the jeep for 10,000 miles with no problem. During that time I put 35X12.50x15's on, detroit truetrack lockers.
Then a woof, woof noise started. Noise is pretty constant, does not seem to get faser or slower at differnt speeds  & getting almost unbearable to drive.
Ive tried to locate problem by lifting jeep and running it. Noise was comming from transfercase, and rear axel moves up and down slightly when running.
The fixes i've tried, I have replaced the transfercase, changed tires back to original 31's, replaced U joints, Have had rearend apart and replaced & axel shaft after breaking one. Replaced brakes, replaced slip yoke. Still getting the woof, woof, and its getting worse. The only thing I havn't done is replace the drive shaft.
Any suggestions!!!!!!!!!  

dang...

hows the rear output bushing in the t-case?  

Not changing in volume or tone regardless of engine speed or vehicle speed??

Sounds like somthing rubbing on something as opposed to something spinning?? Exhaust leak??

Tracking down noises can be tuff.  

2nd transfercase was totally different, pulled the first one to rebuild and put together with engine tranny package I'm putting in. Same noise.  

Muffler is a pile, only 6 mos old and already loose inside. I tied the jeep between two excavators, lifted it and threw it in gear. noise still comming from transfercase area. However driveline does not seem to be running true as the rearend moves up and down as it is rotating.  

my 75 blazer had a noise/vib like that, it was the output bushing in the 203 t-case.. same thing with my 98 burb.

thats almost funny tied between two excavators... LOL  

I thought I was the only one that used a backhoe to pull engines and straighten frames.

I use a tree for my "other" excavator.  

Ive heard "woofs" coming from a bad pinion angle in the back,  check bushings in rear upper and lower arms  

lol, i love my hoe 2!

don't ever piss me off......


 

Thanks, Thats one I had not thought of. I have checked pinon angle but not control arm  bushings.  

if it does it when you're driving, there is a high chance its rear uppers.