Drivetrain ticking

Hello all,
Have a '99 2.7L 4x4 manual trans.
I'm having a ticking under load that I cant figure out. only happens under load/accelaration, nothing in neutral, weight in bed does not aft noise. ticking speeds up as I speed up. don't notice it when slowing down even under compression.
Already replaced carrier bearing (center support bearing on drive shaft), replaced CV half axel, took apart and inspected bearings in knuckles and 4x4 lockers and everything is good. related repairs last six months for other issues, replaced clutch, changed fluid in trans/transfer case/both diffs, replaced upper and lower ball joints, inner and outer rods, UCA and LCA bushings, sway bar end links, steering rack bushings. Noise was there before all repairs and still present is same volume and intensity.
Any Ideas??

 

Check your u-joints in driveshaft.

 

Drive shafts and u joints are all good 4x4 and main. Checked when I did the clutch and center support bearing. Didn't replace so omitted from list. No play and look good. Greased them too.
Thanks though

 

Crazy! I hate that when you hear something like that and can't find it.

Only other time I've something like that was something inside a rear brake drum "ticking" when it turned, but that wouldn't explain it doing it only under load.

 

Thought that too. Pulled both drums off and nothing out of the ordinary.
Transmission?? But why a tick and only on acceleration / drivetrain under load. Not on compression, at least noticeably. And nothing if I'm just cruising at speed. But if I gas to pass I notice it again. Might be there and just not noticeable at speed but if I'm coming to a stop nothing.

 

Yep, I also thought of the tick that you hear sometimes with a tiny leak at the exhaust manifold, but that usually ticks all the time. How bout something like the torque convertor? That would engage during acceleration.

EDIT: Crap! just noticed that you had a manual trans!