I don't hear any whistling with mine, definitely not normal

I also have this whistling and so does one of my colleagues with the same projector. It seems to be normal, I haven't looked into it any further. You can no longer hear it while watching a film. Sending in the projector was too much of an effort for me. For me, there also seems to be something wrong with the fan. Because you can hear how the whistling varies in form after you switch off the projector.