I'm having the same issue too. Specifically with my car stereo, my S7 makes a hissing noise when media is being played through auxiliary cable. I'm still able to hear the music.
My friend got the same phone. We tried his and his phone produces a much quieter hiss, and he can hear music.
I've tried my phone with the Harmon Kardon Onyx 2's AUX port and it didn't make the same hiss.
Any ideas? I'm going to try replacing cable today.