Importing movies from my iphone to imovie - sound issues

I would like to understand why when I import movies from my iphone 5 (ios7) into imovie (version 9.0.9), the sound on some of the videos is either out of synch, or non existent all together. But when I play those same videos on my phone, the sound is fine. I have tried deleting the video's from the event in imovie and trying again, and it still happens.

Also, there have been a few times when I have deleted a range from the event by going to edit and then "reject range", in some cases, but not all, it leaves .1 second of the range in the event. No matter how many times I try to remove that .1 second clip, it wont go away. What is that about? I don't understand.

Please help me.

Thanks,

Sarah