Mocha's the same, she's not afraid of big dogs at all, but when it comes to vacuum cleaners, hair dryers or anything that makes a noise similar to that, she will go running. Over the years, she's grown accustomed to the hair dryer and has accepted that it's something that needs to be dealt with; she still flinches when we bring it out, but she no longer runs from it because she knows resistance is futile.
The funny thing is, she's afraid of the dryer, and only the dryer, not the person actually using it. If you're holding the dryer, she will inch closer and curl up right against you, like "protect me from the dryer, mommy".