The noise was a metallic vibration that only happened while driving and only at a small rpm range. Kind of a heavy metallic buzz or shudder. You couldn't really hear it from inside with the windows up , but with them down and if things were just right, it would really keep it going
. Well, run it under the carport , grab the creeper and a rubber mallet.
The sound made me suspect skidplates, and since I have had the notorious diff. shield mushroom head bolts rattling in the past I went there first.
Sure enough one was allowing a little slack, so I added a nylon washer the each of the rear bolts to tighten them up and eliminate that as a possible source.
At the same time while tapping around with the rubber mallet, I found a few rocks in the transfercase shield rattling around.
After taking the garden hose to all the shields , washing out any rocks that had accumulated, I took it out to see if I had cured it....NOPE...still there
Back under the carport.
Tap , tap , tap, the oil door in the steering/front shield rattles a little , the front license plate is hinged and where it contacts the bumper there is a possible rattle.
I had some of the self-adhesive fender welting left over from installing the Bushwacker flares, so I added that around the edge of the oil door and the contact point for the front license plate. Both are now rattle free.
Out to test it again....STILL THERE
Back under the carport...tap, tap, well you know all that...
Now I am suspecting perhaps I missed a heat shield on the cat or muffler that is loose or has broken weld, maybe a rock stuck in there? Surely it can not be a baffle loose in the muffler?
Tapping the pipe between the muffler and the cat , I find a slight buzzing rattle but can not seem to narrow it down. While trying to get my fat head up high enough to see under the mufflers heat shield I bump my right cheek on the driveshaft, of course the reaction is to jerk and bump my left cheek on the exhaust pipe , searing a nice one inch long red spot (* Note to self*-facial injuries are rather painful, avoid them if possible) Still the sound seems to be closer to the cat and tapping the catback flange seems to generate the best reverb.
So I keep tapping with rubber mallet, and pushing on thing with my hand trying to find a source, when I happen to touch the rear 02 sensor..the reverb stops.
It was loose. I don't know if I forgot to tighten it during the whole plugged pre-cat fiasco, or if it loosened up on it's own. Any way I anti-siezed the threads and reinstalled it , properly tightened this time.
Out for the test drive....Ahhhhh much better!
Moral of the story: When you have a problem look for recent changes that you have made, suspect everything "To err is human".
Oh!... and keep you head low, exhaust is hot
The noise is still there. I guess I should start to lose the mindset that I am bulletproof under 20K on. "IF" my 33s are not delayed again I'll have the front end checked for those possible causes with their install and alignment.