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 )

 

My vote would be something rubbing where it shouldn't. If it wasn't making this noise prior to the transmission being replaced, I would think this would be something the shop that installed the transmission would take care of for you.