New (built) 700r4 rumbles when idling, what could it mean?

[nycxjeremyy]

Hey yall, for reference, I drive a 1990 Chevy K5 Blazer with a 6.2 Detroit Diesel (w/h a turbo) on it

I had a new (built) 700r4 Transmission installed on it a few days ago, and one thing I've noticed is that it rumbles a bit loud when idling and even louder when in gear (reverse, drive, etc)

(This is the 700r4 currently installed on it: https://gearstar.com/gm-700r4-performance-transmission-level-3 )

What could it be? I've driven it around local roads and on the freeway and it shifts properly (1st to 2nd has a very slight kick to it since it is built) but I don't know why it rumbles as so, any input would be highly appreciated

(Video: https://www.reddit.com/r/Squarebody/s/g806b79N8Z )

 

[Wes Harden]

Have you double checked the t case position. It could be in 4wd. Also I would inspect driveshafts for loose bolts, bell housing bolts are tight, along with the cross member

 

[Blue85]

I take the video to be idling at a standstill, which makes me think something is hitting. It's possible one of your torque converter bolts is loose and has backed up far enough to buzz on the transmission. Maybe you got a new transmission mount and the swap wiped out the engine mounts or something like that. The harmonic balancer could be rubbing on the crossmember or the exhaust pipe hitting something since the engine moves when you put it in gear. Or it could be almost anything rattling against the floor. Give everything a good inspection. Climbing around while it's running should help you figure out where the noise is coming from.

 

[Greg Ducato]

I would think loose converter bolts or even a broken flexplate