A new hum or whine usually means worn bearings, a rattle usually means a loose mount or coupling, and a gurgle usually means condensation collecting in the pipe. None is dangerous, but a failing fan should be replaced before it stops.
More detail
Condensation is routine in Central Ohio winters, when warm, damp soil gas meets a pipe running through a cold attic or up an outside wall. Ohio's standards require the piping to drain that water back down to the ground beneath the slab or membrane and require fans to sit in vertical runs so water cannot pool in the housing; a sag in a horizontal run defeats both. Vibration noise usually traces to the mounting, which the standards say should limit transfer to the framing, or to couplings that have worked loose. A fan mounted inside the living space, which the current Ohio standard does not allow, will always be louder than one in the attic or outdoors. See the fan replacement guide.