I was wondering if the sound would go away, but I am unsure. The sound really sounds like a thin plastic sheet or membrane behind the keys that maybe isn't glued down or isn't supposed to be in there. The noise has been getting slightly worse over the last day or so. The floor model at the t-mobile store sounded perfect and had a nice click to the keys when pressed with no crunchy plastic sounds when you touched it.
I can't speak for the upgrade cost difference, but the full price I paid at radio shack was $600.86 out the door ($550 + tax). At T-mobile they have the contract free version for $499 so it will likely be $550 out the door (there might be a rebate involved in that price). This was in the San Jose area in CA.