Need to Sync Audio to Timeline

I dragged an audio file from my Adobe Stock library to the timeline and it will not sync. The first time I did this the clip synced up perfectly and the audio clip ending synced with my last video frame. However, when I changed audio clips and dragged the new one to the timeline (after deleting the old one) the new one will no longer sync with the end of the video. See the screenshot.

Also, can anyone tell me why black boxes are at the beginning of each video clip?

I'm a newbie to PP so any help would be appreciated.