What is this noise?!

Hey guys I'm new to the group and have a question about my 2010 model with the 4.0 v6 auto. So this thing makes a noise in what I'm guessing is 4th gear and it only happens when you're just barely cruising along mainly between 40-50 and barely having your foot on the gas pedal. It's hard to describe the sound but to me it sounds like the engine is kinda lugging but it's definitely not a normal sound. If you press the pedal on down while it's making the noise it'll stop. I know this is a vague description but do you guys have any idea what this may be?
 
Hey guys I'm new to the group and have a question about my 2010 model with the 4.0 v6 auto. So this thing makes a noise in what I'm guessing is 4th gear and it only happens when you're just barely cruising along mainly between 40-50 and barely having your foot on the gas pedal. It's hard to describe the sound but to me it sounds like the engine is kinda lugging but it's definitely not a normal sound. If you press the pedal on down while it's making the noise it'll stop. I know this is a vague description but do you guys have any idea what this may be?
Rear end gears ,they whine under power but let up when you let off the pedal. A axle bearing will growl all the time .
But could be a bearing in the tranny