Could be the bearing going bad (running out of lubreication), the pedal itself is hung up on something, or squeaky slave cylinder.
If the sound consistently changes with temp change or if the sound doesn't go away - I'd take her in. Your under warranty and I wouldn't want to wait for it to potentially get worse (probably nothing wrong, but you want it to be logged in the system as such). Being logged into the system can help alot. If something pops up later, bringing it in and complaining about it - even if nothing is found to be wrong at the time, could become useful later (happened to me = free clutch replacement at 35K miles).