When I create a composition in after effects and try render in media encoder in mp4 the audio is repeated every 1.5 seconds. Like a crazy loop.
Why does it happen? My after effects is at version 2015.3. Tk
Those are bugs in current versions of AE. Render an intermediate file liek an uncompressed AVI or MOV directly from AE and compress it later in AME.
Or simply make your composition a few seconds longer and trim your work area to the actual length you want the video to be (make sure there is an audio layer for the whole composition length though - even if it's a silent layer).
This issue is fixed in the After Effects CC 2015.3 (13.8.1) bug-fix update. This update, available now, can be installed using the Creative Cloud desktop application, or by choosing Help > Updates inside any Adobe application.