So I go to start my truck Tuesday morning and I hear a loud knock while it's parked with the ac on and idling.... I put it in drive and the noise dissipates now immediately I'd thought I had spun a bearing but what is weird is that when I park and turn the ac off their is no knock and the compressor is good on the truck so I'm really at a loss any ideas ? The noise is definitely coming from the bottom end it seems, any suggestions btw all fluid levels are fine just changed the oil Friday night and the level was fine before I changed it

 

I am wondering if it is not a broken flex plate.

 

I think you may be on to something, gah I just replaced the trans last summer I really don't feel like dropping it out again....getting a second opinion from a guy on monday and then to decide what to do, I think I might just dump the truck and pick up a new trailblazer who knows

 

was a broken flex plate, took me 5 hours to take off the transftercase and drop the trans and slide it back and remove the flexplate replace it and put the trans back and put the transfer case back on woooo fun times I tell you ugggggggg

 

Damn! I scare myself sometimes! LOL

Glad you got it fixed!

 

Seriously, Swar.. Thats sick. You should have a PH.d in Blazers, That was rediculous how you just picked that out of the air.

 

I wish it was out of the air. I experienced the very same symptoms on an old 85 S10 2.8L 4x4 that I had. What a pain! The flex plate broke right after putting in a rebuilt transmission in. So I had to go through all of that mess twice (removing and reinstalling the transmission that is)! I ended up just using two long bolts to push the transmission backwards enough to get at the torque converter to crank bolts.