The Epson projector is about in the middle of home theater projectors in terms of noise. It is generally quieter at full power than just about any DLP projector, and usually a fair bit quieter. It's on the high side of average in noise, among the other LCD projectors, and the LCoS ones as well.
Epson claims 22db in low power, and that's believable. Figure about 27 db at full power. To put that in perspective, I believe the quietest projector around is 18 db at full power, and the loudest DLP's run around 32 - 34 db.
Epson's dynamic iris makes a low rumbling noise that isn't very loud or noticeable in my opinion, but I do know that it bothers some folks. I rarely, if ever notice it when the Epson is in the main theater - about 4 feet behind my seat. In some cases, I believe mounts or a rear shelf can resonate a bit with the low frequencies. I've noticed that by putting some soft drink coasters between the projector and the table it sits on, helps reduce the rumbling. Again, however, it is low frequency and to me definitely a lot less noticeable than the fan noise.