Weird noise coming from engine. Please read!

[OC Stroker]

I have an 08 6.4. Just hit 80K and has been Spartan tunded for the last 60K or so. When the torque converter locks, at times Ill hear a low ringing sound coming from the engine. It almost sounds like the noise you'd hear form brakes when coming to a stop. The sound also happens when accelerating or if I let off the throttle during accleration before a gear change (doesnt necessairly have to be under hard acceleration). This sound will only happen when the truck is fully warmed up.

Ive taken it to the dealership and they replace the tranny under warranty. That didnt cure it...Next they replaced the egr cooler...That didnt cure it either. I just took it back again for my 80K serivce and they cannot figure out what it is.

Any thoughts? I dont think its affected the performance of the truck but it sure is annoying.