Voltage needle wobbless at low RPM - problem?

[aweiss2k]

I recently noticed that when I idle my truck, the voltage needle will start to wobble when RPM's get around 1200 or below. As soon as the RPM's get above that, the needle stops moving. I haven't noticed any other symptoms or problems, likely because the alternator is providing adequate power 99% of the time. Nevertheless, should I snag a new one and pop it in, or just let it be?

Thanks,
Aaron