Many of those water heater power vent motors generate more noise as they get older, some of them are very noisy from the beginning. If the noise level increase is noticeable it would be wise to check the motor / blower assembly. It might be the motor or / and the blower blades.
The whole assembly sometimes becomes loose (because of the constant vibration) and it might just require re-tightening. In some cases it’s the blower blades touching the enclosure which creates some unusual noises. Touch the motor blower assembly (be very careful not to get burned) a few minutes after it starts operating. If it is very hot you should have a professional look at it.
As for the reddish-brown ooze, regular power vented water heaters (not condensing type) should not produce any moisture. It might be some rain water that traveled inside the PVC vent pipe and caused corrosion of the motor assembly components… Right above the water heater means at the first joint, where the PVC vent pipe connects to the blower assembly?
Water heater’s PVC vent pipe termination end should have a rodent screen installed. Without it, a bird or any small rodent capable of reaching the pipe can enter it.