The quietest noise level of projectors that were launched around the same time as this projector is 27dB and the loudest is 48dB. At only 30 decibels, the NEC M403W has a quite quiet noise level compared to most of the other projectors that have been around for a comparable time to this projector.
Alternative 30dB noise level projectors currently available that you might want to consider include the NEC M323W (£735.42) which is cheaper.
If you would consider a projector with a louder noise level then you might want to look at the Epson EB-575W (£880.79) (35dB and cheaper).
What does "noise level" mean?