There is a bug in personalStudio 1.5 (which will hopefully be cleared up in a future release) that causes audio levels to double whenever two clips are played simultaneously. Also, when laying a video clip with muted audio over a background audio file, you may lose your right stereo channel for the duration of the muted clip.
Here’s a workaround: Create a blank title and place it on a layer higher than your video (e.g. layer 6). Stretch the blank title to the length of the entire
project. This will completely eliminate volume changes during transitions and regain your lost stereo channel during muted video clips.
Another bug to watch for: If you place the blank title layer below the video layer (e.g. layer 4), pS will ignore your muting of the video clip and the sound will be present.