Hi Jules,
The way the IBIS behaves is as follows. I usually have the setting Menu E -> "Half Way Rls With IS = ON", unless using the LCD as main viewfinder, usually operating the shutter release with the touch panel.
I also set IBIS that way but I don't operate the shutter with the touch panel. I don't see how you can have Half Way Rls using the shutter panel.
When I half press the shutter, a low volume, high pitch sound is emitted, I think it comes from the gyro(s) spinning. That sound has been there all the time, on all cameras, pre- and post repair. The sound was more pronounced on the first camera body (the one that got stolen) than on the second one, but has never really bothered me.
I also have some humming and I believe it is normal. Same with the EM-1.
Within a fraction of a second the image in the viewfinder stabilises. The result is noticeable, when using magnified viewfinder the ability to focus and evaluate the finest details without shake is stunning.
Same here.
The times I have had the IBIS engaged for instance when panning/following subjects, would be typically 10 seconds, one minute at most. I have never heard any clac-clac sound, and have never experienced the (healthy) IBIS disengaging either. If the IBIS is set to continuously work I would turn off the camera between pictures (to save battery and reduce heat dissipation).
IBIS is not made to be used when the camera is not moving at all, like on a tripod - I don't think is is wise to keep it engaged for a long time, like 1 minute. This is why I pre-focus without IBIS. I don't see why you would set IBIS to continuously work since it is only useful when focusing - IMO, this is looking for trouble.
I have been extremely happy with the IBIS performance, until the faulty behavior, manifested by humming/vibrations, after initial stabilization the IBIS disengages within a section, clearly visible in the image in the viewfinder.
I have used the camera with scopes requiring the focal length to be set from 500-1000mm, and the higher the setting, the more frequent/pronounced the behavior is. If I set a low value (lower than required e.g. 300) then the IBIS will stay engaged, but at the expense of less IS taking place (also visible in the viewfinder).
I set it for 600mm or 900mm when using the TN. Sometimes I forget to change the setting and it does not seem to matter.
I will provoke a full reset by removing the battery 24 hrs (according to guidelines from Olympus support) and keep you updated of progress. I may be a SW defect, some calibration parameter that is set incorrectly and causes the problem, and that will be reset to default value after reset. Fingers crossed...