I took mine to the dealer and here's what they found/did:
Loose bolts and seat alignment tabs. Could feel movement in the seat rail. Tightened seat bolts and test drove, noise lessened. Removed the seat and cut of alignment tabs from the seat rail. Test drove again and could not duplicate the problem. T-SB-0288-08 OP Code NV5011 for seat rail alignment pins.
This was fully covered under the 36,000 mile warranty (which expires soon). I'll wait and see if it comes back or not.
Is your seat an auto or manual adjust? THanks!