Navi tells you the same thing everytime you turn on the game or waste enough time.
I didn't find her that bad to be honest.
I agree with Crash, she didn't "Hey" that much I thought and I liked the "Watchout"s just became par tof the background to me in the end, it was nice to have her 'watch my back'... Link needed a companion haha.
I found Midna's laugh coming out of my Wiimote to be much more disturbing!
I'm playing TP at three in the morning in my livingroom with the sound turned down so it doesn't wake my partner up then a deafening "Hee-hee-hee-haa-haa-haa" comes blasting out the Wiimote!
Made me jump loads!
To be honest I find Fi more annoying that Navi.