Drivetrain clunk

[W37V]

I know it's not right forum, but this one seemed more active than f15, so I just wanted to post in here for higher visibility.

Car: 2015 X5 35d

Before my warranty expired, I had my X5 checked out by a dealership. They found a small oil seep from transfer case, so they replaced it.

Since transfer case was replaced, there is a clunk in the drivetrain. The clunk happens during power transfer - when i apply accelerator and let go - at lower speeds.

Dealership replaced the transfer case - again, but the clunk is still there. The noise sounds as if sometimes is coming from rear, sometimes front, but mostly from the middle.

Not sure if related, but I also heard a thump - like something hit a transmission tunnel, while entering a neighborhood (90 degree curve). It sounded as if the hit was under ashtray / cupholders.

Today, I refused to take the car home, as they never fixed it. Any suggestions what it could be? Thanks