200 RPM? What's it normally at? If it normally sits at 2500 or so RPM, that seems fine, as the voltage always drops a little...if it's more like 4000, you're just being paranoid 🙂. If it's around 1500, then maybe you have something to worry about...but then again, typically below 2000RPM or so (and some higher), they lose a great deal of accuracy, given that 99% of people using one have a 3000+ RPM fan.