Weird noise from transmission

[motortusmc]

My 2016 GMC Sierra is making a weird noise from the transmission. So far seems to be only in Park or neutral. Almost like a buzzing noise. In addition to that it also has a hissing noise when I switch from park to drive or reverse that goes away when I hit the throttle 

 

[rav3]

That almost sounds like a belt pulley bearing that's out of grease & needing replacement. but that's me...... I'm sure others will chime in. How many miles? Engine? (5.3) Transmission? (6L80)

[motortusmc]

5.3 engine, I'm pretty sure 6l80 trans. It's the loudest in my opinion under the transmission. Kind of hard to pinpoint exactly where it's coming from

 

[diyer2]

mechanics stethoscope, cheap tool

[rav3]

 

Edited October 9, 2023 by rav3