Need help with a 2015 Freightliner dd15 harmonic vibration

I've been trying to track down a harmonic vibration since day one with this truck and it's been a battle.

Over past 2 years with it I've done 6 alignments,replaced tires almost 3 times because shop says it's the super singles, balanced all the tires every time and put centramatics on all the tires, the drive shafts was sent out because it was out of balance, U joints and carrier bearing have been replaced, we found this weekend a broken engine mount, a broken cab isolation bar bushing, a bad suspension air vavle, and the rear axle hangers were put onbackwards. I have replaced all the shocks 2 months ago including cab shocks, now the right side cab shocks is blown.

All of that and still this harmonic vibration is there. Truck only has 209k miles on it and it's been there since day one.

Here is an audio file of what the vibration soundslike in the cab while I'm driving. It comes and goes usually when I'm adding power gradually to theengine and it's the most pronounced around 50-70mph.

Nevermore, can't add a sound file. Here is a link to the audio. Also, here is video of the truck on the dyno

Any ideas or help, please!

 

No. I can let the steering wheel go and it'll go a good couple miles before it starts to pull to the right.

I don't feel the harmonic vibration in steering wheel. What you hear in the audio file is coming from the back of the cab.

 

Played with the ride height and still no change. Tires have showed nothing for wear patterns.

 

That had been checked a few times now, though I'm not sure how they missed the rear axle hangers being installed backwards this long. That changed the angle by 1/4".

I truly think it's in the engine at this point. Not sure what it is though. What leads me to belive that is it's not a constant vibration, it's only when I start to slowly add power to the engine or maintain just a little power that it does it.

 

The big part is the loud slapping noise, but it wasn't until I made the recording that I noticed the underlining low harmonic sound.