I suggest to use the very noise that your camera captures and blend it with the photograph.
point your camera against a white object (e.g. wall, door)
The automatic exposure should stop down the lens until the white becomes a mid grey.
capture as long as you need
In your Editor, blend the grey noise with the photo by using a layer blending mode like "...
What do Audition/Premiere show as the bit-rate of the audio file in the original source video? What do iMovie/Premiere show as the bit-rate of the audio file when imported back in?
Sounds like possibly the source video is indicating an incorrect bit-rate, i.e. actually recorded at 48kHz, but being identified/treated/exported as 44.1kHz in Audition, which ...
A good option is Davinci Resolve.
It has a specific feature called Retime controls, where you put a couple of markers and select the speed of that particular segment.
90 Minutes is quite long, you probably want to make some proxy videos at smaller resolution and then render using the original clip.