Nasty loud buzzing/grinding noise coming from underneath the truck, and seems to be from the trans area while driving. Anything more than light throttle input gives the noise which will last about a second or two then go away. Didnt get on it at all for fear of having to be towed again. Seems more like trans to me? Also entertaining the idea a cracked stock flexplate. Motor seemed to be okay but you never know. Thanks.

 

sounds like flexplate, look through the inspection port with a flashlight and mirror check around the bolts, if no signs of cracks then move to transmission !

 

Just an update, I pulled all the turbo stuff off from the underside and removed the converter inspection cover. The flexplate appears intact. So the noise could still be the transmission or the torque converter but I'm leaning towards the trans. Noise only happens once everything get well up to temperature. From the dipstick the trans fluid is cherry red, smells normal. Next step I will drop the trans pan and see if there's anything going on in there like metal debris or a clogged filter. Thought I could get away with a stock 4l80e, guess not.

 

do you have a 1 piece or 2 piece drive shaft? my dads did the exact same thing you are describing, and it was the carrier bearing on his 2 piece driveshaft

 

2 PC shaft. I visually inspected the driveshaft and also checked the u joints. Everything was tight but I'll give a second look to the center section when I get back under it.