Picked up a 2016 Chevy Silverado Z71 a few weeks ago, truck has 135,000 miles. Little info on service records. New tranny according to my shop. They couldn’t figure the noise out either.
It is a rotating clank noise coming from the center of the truck that seems to be linked with the rpm’s, (a little more throttle in the right conditions and the noise speeds up, let of the throttle the noise slows). But it only happens under very slight throttle while the engine is under any form of “load” going up a slight grade for example and trying to keep speed is when the noise occurs the most. I can also get the noise to happen on a flat if I go from an idle cruise (30mph) to just slightly pressing on the throttle to gain 1-2 mph, but it consistently will do it on a slight grade. The noise stops when you press the throttle down just a tad more or let of the gas. It seems to have a threshold of “load” to throttle that makes the noise occur. For example on a steeper grade I can get the noise to happen with more throttle before it pushes past the “threshold(essentially it will happen thru a wider range of throttle modulation)” and it sounds faster and louder compared to when I am making the noise occur on a less step grade. (Range where the noise happens is smaller.
vid of the sound attached

Any ideas, input or advice would be greatly appreciated.

 

Speed also affects the intensity, the vid attached I’m going about 40-45 and the noise is way worse compared to when I am going 30-35

 

Could vacuum have anything to do with it, I’ve also noticed the brakes seam to be really hard to press when I am stopping at slow speeds. For example rolling up behind someone at a gas station at 3 mph and then going to brake it feels like the booster is not working. I am away their is a vacuum pump ran of the belt to provide vacuum. Is vacuum factored into anything to to with the tranny or am I dealing with a separate issue.