Vertex 180 Skimmer - Noisy again

[newreefer_59]

Bought a Vertex 180 Skimmer in February and before long it seemed to get noisier than upon initial set up. Called the supplier about 2 months ago and they immediately sent out a new impeller shaft that was an upgrade. It seemed to do the trick, but the last few days the unit seems to be as noisy as it was before the replacement. Do I need to clean the shaft and motor unit every month or so, and is that the cause of the higher-than-expected running noise level?