it all has to do with being able to detect and understand all the sensations the world brings. some of us have sharper or duller senses and when your senses are sharp and your brain has just learned how to pay attention to them, the world can become a scary place when a noise starts. (have you ever seen a bunch of five year olds listening to a band with their hands over their ears- they are still working on making sounds work better for them!) babies haven't got the brains to know that the noise isn't a threat or that it will end as soon as its clean under the coffee table!!!
i would stay with her whenever possible when scary noises are happening and they can't happen when she isn't around. instead of letting her cry a bit when a noise is scary to acclimatise her, find fun noises that she can enjoy with you or even noises that she can make! being in control of a noise is a good way of having it be more fun. if the blow dryer is scary what about a small fan? etc. support your dd with things that are just bearable rather than things that are scary and be there with her. (you may find that if you DO let her cry a bit to get used to something that her her brain that can't think her way out of the fear actually lays down pathways associating sounds with fear for much longer!)
as she gets bigger and learns to tell herself that the noise won't be there forever, that mummy and daddy are near and won't let the noise hurt her etc, then her brain will start to help her pay less attantion to the noise that bothers her so much now. for right now its a pain but by being sensative to her needs, your daughter will get better about this.
( BTW, there are also a group of kids who love noise! (my son is one of these). while this may sound fab right now, he likes to do lots of happy screams to create noise when he is bored so there isn't really an ideal situation!
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HTH!
