I am not telling any secrets here when I tell you that hand dryers make noise. But some bathrooms are in more noise-sensitive locations than others. So how noisy is too noisy and what options are there for quiet hand dryers?
Generally speaking, if noise is a very important issue for you, there are very few options. Usually, the faster the hand dryer, the more powerful (and loud) the motor has to be. Also, generally speaking, if you add some kind of noise diffuser, it will increase the dry time (everything in life is a trade-off!).
Also, be careful of the listings for decibels. They, like dry time, are difficult to measure and there is no standard protocol. Most of the time, companies measure the decibel levels by simply turning the machine on without any hands in the air flow. This measures the motor noise, but doesn’t really measure the dryer noise while in use. Hands-in can add many decibels.
I would always evaluate the environment of the bathrooms. I was once working with a large university that wanted to try out hand dryers. I suggested that the tests be conducted in the Student Union or some bathrooms with high traffic and low noise sensitivity. Don’t try to put them near the professors’ offices in those old buildings. You are inviting complaints.
That said, people who are near bathrooms with hand dryers do, like anything, get used to the muffled noise. It is no more distracting in today’s cubicle world than conversations or other, normal background noise.
You should note that we have never come across any hand dryers that exceed the OSHA standards, which is that noise becomes dangerous (and hearing protection is required) for noise exposure of 90 decibels or greater for over 8 hours. While there might be hand dryers that can generate that level of noise, I sincerely doubt anyone will stay in the restroom for that amount of time!