I have this same sound. I assumed it was one of the tires in the front but haven't really put much effort into sourcing the problem yet.
If it's a rotor or rotors you would feel it in the brakes pedal rather than hear anything.I have a 2006 Frontier CC 4x4 with about 42k miles. New tires and alignment about 2k miles ago. Drives very smoothly, no pulling or vibration.
However, I've noticed that when I am slowing to a stop, even on relatively smooth roads, between 20-10mph I will hear what sounds like a wobbling sound which appears to come from the front end. There is no vibration, pulling, or any other anomaly that I'm noticing. I am starting to think that it may be slightly warped rotors, though I'm not noticing any vibration or pull in the steering; however the dealer replaced the front rotors once before (under warranty) because they noticed that they were warped during a state safety inspection.
Any other ideas? Could this be suspension related? Is it normal?