I have faded out an audio track by using first keyframe in o.00 dB and some frames later the second keyframe at -48 dB, so the basics. Still, I can hear the sound after that keyframe and even in the soundwave is showing. I need to fade out the audio completely so that there is no sound, but this is still happening. Please take a look at this screenshot. You can see thet the soudn is faded out to the maximum, -48, and still you can see sound and hear it. Any help will be much appreciated!
What version of AE are you using? If it's 13.5.1, try it in 13.2.x and see if the issue persists. (You can open a CC 2015 project file in CC 2014 with no problems.) If it's 13.5.0, consider updating to 13.5.1. If it's 13.1.x, consider updating to 13.2.x
I bet you can get that down to -85 db just by typing it in. Maybe even lower. Sometimes the sliders in AE DO NOT represent the minimum & maximum values. And you can always trim the audio layers, too.
But I gotta tell you -- AE is really a lousy choice for doing any kind of audio work. It really stinks at it. You should be doing that stuff in a different application (like a video editor), and using audio in AE just for reference.