Merging threads means that a Moderator took two duplicate threads from the forums and merged them together, so that we don't have two separate but parallel discussions going on.
Safe Mode temporarily disables all 3rd party apps you installed. This can help narrow a problem down to something you installed vs a system or preinstalled app. Since the crackling stopped in Safe Mode, that implies that some app you installed is causing the problem -- but the challenge now is to figure out which app. Unfortunately, there's no easy way to do that, besides uninstalling apps one by one and seeing if the problem goes away after each uninstall.