DD (2.3) literally jumps at any little sound. When shes playing in the garden and an airplane goes by, she runs inside.
When the fridge/cooker/alarm clock beep or make a sound, she looks startled and says "whats that noisy mummy, whats that noisy?" - repeatedly, and I have to reassure her at least a dozen times a day.
She was terrified of the sound of the bath filling after we got a new bathroom fitted, because the bath is bigger and the taps are the waterfall type, so make quite a racket, and she would run away crying and wouldnt bathe in it for days. After much cajoling and reassuring, she stands watching the bath fill and plays in it happily now.
I just went to find her because she wasnt playing in the garden as I thought she was; she was very carefully and quietly climbing the stairs ( to goto her room, Im assuming), and I said very gently "DD...", she cried out in alarm, and then burst into tears!
Otherwise, she is a very happy and bright girl. She is non-stop throughout the day, can hold a decent conversation with anyone, and needs constant stimulation to keep her engaged and interested (think paints, crayons, sandpit, pots and pans, dollies, books shes never seen before, my iphone, anything I can get my hands on...) - which if she has, is an angel to be around.
However, after this most recent little outburst, I am a little worried now, as to why she reacts like this to noise.
My ds is 4 and still not totally comfortable in loud, busy situations -but when he was 2 yrs old he would sometimes cry if we even sneezed loudly! your dd sounds delightful and you are doing all the right things so don't worry, she will adjust as she gets a bit older
My DS is similar - strange/loud noises can terrify him. I can't take him to any toddler music playgroup type activities as he screams in fear and makes a run for the door! I surprised him on the stairs recently as well and he practically jumped out of his little skin. It doesn't always make sense though as some things I thought would have him petrified don't bother him at all (loud machinery, close up to jet engines, sirens), it is quite eccentric like you say! Last weekend sheep bleating made him scream in fear, yet he loved the goats