WS-8-150-DC Fan 0 - 8000 RPM

[bajaconnect]

On the bench the WS-8-150-DC switch fan turns on to 8000 RPM then off again after 3-4 seconds later and repeats none stop, on off, on off. its in a room thats about 25C, i have another similar switch in the same room that runs my home and its fan is off and acts in what i consider normal operation.

I tried updating the firmware to latest beta, no change. i have several of these switch's in operation and i've never seen this before?

Any ideas?