Audio and Video not in sync

Report · May 04, 2018

I did the following to remove noise in the video file.

1. Imported video file into Premiere Pro, added that into sequence panel.

2. Exported sequence as mp3 (as 128 kbps) and stored the Audio file (say - Audio1.mp3) alone in one location

3. Opened the stored audio file (Audio1.mp3) in Audacity and removed noise; and exported (as 128 Kbps) this noise removed file from audacity (Audio2.mp3).

4. Now, imported this Audio2.mp3 into Premiere Pro, added this into A1 track (removed the old audio from A1 track).

Now, i see there is difference in length of audio and video. Why it is so? I checked the length of Audio1.mp3 and Audio2.mp3 in Audacity, and both are same. Why it differs in Premiere pro.