2014 Cascadia freightliner humming sound driving me crazy. Help me find it.

OK truckers/mechanics! Hoping one of you really smart Awsome essential Truckers can help me out Let's see how good you are lol. I havea 2014 Cascadia freightliner. 13 speed. Yesterday I did a drop and hook Pick up an empty trailer noticed a humming are whining sound from what I thought was coming from my throw out bearing. I grease it that really didn't make any difference. Plus I had the clutch changed out this summer. It's almost impossible for me to tell exactly what direction the sounds coming from. But here's the thing, It's not consistent in only happens when the trucks moving down the road it only happens when I begin to accelerate or when on cruise control and it just barely starts to go up the Hill just before it picks up speed. It seems to be in line with throttle but not really speed. May be more with the boost. So it hard to explain but if I climb a hill goes away going down hill or flat comes back but I speed up with throttle it goes away. Also this may be a factor I am smelling exhaust when open my door. May of lost exhaust clamp. I'll find out in the morning. It doesn't make any noises at idle has to be working (OK WHAT YOU GOT) I am lost

The only thing consistent is on flat or down hill with little torque it comes back. But if I increase speed/ with throttle it goes away. Also nothing if bobtailing or under 20 mph.

 

Yeah transmission

 

Well mine was a big mistake on my part.
So I had oil pan gasket leak I had already bought a gasket and a oil pump and intended on charging them that weekend coming up. On Thursday I noticed what I thought the leak had got worse I checked my oil and it was fine jumped under my truck couldn't see a leak figured I would keep eye on my oil level and go as planned to change it in couple days. Turned out it was coming from transmission cooler line had rubbed a hole in it drained all my oil burned up my Transmission had 1 million on it so I wasn't to pissed. But it was about $10,000. But if you're having the same thing check your oil before it's to late.