Anyone Know The Cause Of The TRXL Series To Have Gear Whine?

[bamlogisticsinc]

What causes it? Just something i noticed. 5 Speeds, 6 Speeds, 12 Speeds is what i noticed have that same sound, But the T2000 Series to NOT have that sound. The TRXL series seem to have a "gear whine" to them. Even the airshifted models have that same sound.  

 

There is also a noticeable loud fan sound kicking in at 4th gear. 

 

Anyone knows what causes it as opposed to the T2000 series? I would assume straight cut gears...

Also, I would like to know if the Overdrive TRXL1070 has more of a "gear whine" than the TRXL107. 

 

Lookup "Appalacianrust" and his 1980 Mack R model hay hauler. That has the same noise im talking about. 
Heres an example, (by no means promoting his content, if thats against the rules, just a genuine question) 

 

[Vladislav]

Good question. I would like to hear the answer too.

[Freightrain]

I have watched YouTube videos of rebuilding a Mack.  Yes, straight cut gears just like the early 9513 that whined horribly.  I can't see why the OD would cause more whine?

I would say the tip turbine is making more whine then the transmission.

I have a 5 spd outside covered in a foot of snow right now.