Banging from passenger floor when downshifting. Please help!

Hi all. I have a 2007 Taco, V6 6sp with 75k..
Whenever I slow down from freeway speeds and downshift from 3-2 or 2-1 and fully take my feet off the pedals i hear a loud bang coming from the passenger floor area. The speed that this happens ranges from 2mph-35mph. Its been at the dealership (Subaru where i purchased it) under warranty for about a month now, and will be goiong to a Toyota dealership Monday morning. Subaru has already replaced the driveshaft, U-joints, body mounts, upper intake hose (from a TSB). Now theyre telling me that it's a "natural noise"... BULL!!!
I was wondering if any of you guys have experienced or have heard of this issue/ have a solution. Any tips to let them know would be appreciated.. I just want my freaking truck back