Pulsating harmonic vibration with throttle

[alvocado]

I'm looking for help diagnosing a new issue. 2011 Yukon, 185k miles, in excellent mechanical condition. While doing about 2000 miles over the holidays, I noticed a harmonic pulsation with throttle application. It's most noticeable at highway speeds but also evident at low speed around town. The pulsing stops when I lift off the gas. The truck is in 2WD so no power should be going through the front diff although I ran it in both auto and 4hi during the storms around the holidays when I first noticed the pulsing. 

 

I don't get any change in noise when turning which rules out a wheel bearing but I wouldn't suspect that based on the condition only presenting under throttle.

 

My only thought is a potential driveshaft u-joint since they are factory original. In the past, a failing u-joint would cause the occasional drag or hanging up of the drive shaft while driving but I haven't experienced that.  

 

Diff, transfer case and tranny fluids have been changed every 50k miles. 

 

Any thoughts are appreciated.

[CamGTP]

On throttle vibration would be something in the driveline so you are on the right path. For sure be checking the u-joints.

 

On FWD cars it's always a CV axle when you get on throttle vibrations.

[richard wysong]

May be the torque converter if the driveshaft checks out. Pull the driveshaft and check for a frozen or worn u-joint, check the transfer case is actually in 2WD, check the trans mount

[alvocado]

The u-joints checked out OK with the driveshaft out of the vehicle. I can feel the 4wd and auto 4wd engage and disengage so I'm ruling out a bad drive selector. I don't get any pulsing through the seat, it's all steering wheel which would indicate something up front. While it's most noticeable on throttle, it's still present after letting off the gas. 

 

Aside from a visual inspection of the boots, what's the correct way to check the CV axle? 

[richard wysong]

How are the motor mounts? where you get the vibration in the steering wheel I would take a hard look at the left side

[alvocado]

The left mount was replaced 18 mos ago. When it failed, it was visibly leaking fluid and there was a hard clunk when coming to a stop as the engine shifted.