There's nothing wrong with the speed of the audio. It probably seems slow to you because you are used to the PAL versions, which are sped up by 4% (from the original film speed of 24fps to 25fps).

In NTSC (that is, true interlaced NTSC), the conversion from 24fps to 29.97fps is accomplished by 3:2 pulldown, which doesn't result in any change to the actual speed or pitch - it basically creates extra frames between the actual film frames by means of interpolating and field-blending.

It's all about your frame of reference; since you've seen the PAL versions for so long, you're accustomed to the movie running 4% faster than it's supposed to.