Great Beamer - unfortunately after 50h increase in volume - third projector series then properly

I bought this projector because of the very low noise level of 24dB specified in ECO mode because my BenQ W1070 had made too much noise (Beamer is directly above the auditorium). The TW6100 was wonderfully quiet as I set it on the ECO mode (normal mode, unfortunately, much too loud).

Mounted on the ceiling, ran. Super image was subjectively neither better nor worse as compared with the W1070 (nice of wegbleibende rainbow effect was compared to DLP W1070 (clear is TW6100 indeed an LCD projector). The auto iris had to disable it, because here the creaking was very clearly heard the fan was only heard if you look strongly suggests concentrated and even in very quiet or silent movie scenes (yes, there are also films on which is from and even listen to no sound).).

50 hours later I turned on the projector (after two weeks in possession) and after the initial short, strong and noisy fans turning (was always so, for about 5 seconds) RECOURSE made a rather unpleasant sound. It did not sound entirely by fans but more like a hum, but which was very disturbing.
Have measured the noise in ECO mode at once 35db. Living room where the projector hung has always been quite cool (wrap us better times in a blanket), Non smoking and no large dust in the room. Have changed the settings and reset, made the projector normally, cable is disconnected.
Unfortunately, all this has been of no avail, Beamer remained disturbingly loud at 35dB and one was always happy when he was off again. The next morning, I again turned on him to see if the problem persists - the same in the evening, no improvement.

Then I returned the projector again and now waiting for the refund. Although it may possibly have been only a Monday device that "confidence" was disturbed - that's why I'm going to get the TW3200 which has long been on the market and from the known no noise problems.

Update 30/07/14: See my comment.
I've now bought this projector for the third time a few months ago, this works just fine (for five months) and is barely audible (deep fan noise).