Weird sound/pop-up issues after Android updates on new Galaxy S5

[AC Question]

I lost my previous Galaxy S5 for Verizon so bought a new one. Everything worked at the start, but then the updates began and the sound now is both very low and filled with static and cracking noises (only when using wired headphones, speaker is fine).

Also, when I change the volume once in a while Google Voice recognition pops up even though I explicitly turned it off in Settings.

When I cleared the defaults, changing the volume pops the box below: "Do you want to open with Google App or S Voice"? So seems that the Mic is reacting to the audio when the headphones are in.

I tried the following to fix this problem without success:
1) Cleared the cache partition
2) Removed and inserted back sd card, battery, restarted the phone
3) Did a factory reset
4) Disabled/enabled Google app, re-installed the key apps
5) Started in Safe mode - same issue persists.

Any ideas would be greatly appreciated!

 

[srkmagnus]

Does the crackling noise happen with all headphones or only a particular set? If it's all, then I would suggest asking for a replacement as that unit may be defective.