I recently bought a Zotac 980ti Amp! Extreme and it is exhibiting some weird fan behavior. The fan tachometer in Afterburner show spikes (of about twice the fan speed) every 2-5 seconds even though the fan speed (in %) remains constant. Is an issue with the reported fan rpm or the voltage supplied to the fan? It doesn't seem like the fan speed actually changes, at least not from what I can hear but the rest of my pc is kinda loud. Not sure if I should try to send it back or not, I'm very satisfied with it otherwise. Seems like a common issue with the models from Zotac so sending it back probably won't help much. This was posted on another forum. Mine looks about the same.
I think the spike is too short for the fans to be able to spin up. They don't seem to react at all, I can't hear or see any change in fan rpm. This is how it looks in afterburner: