Question: Recently I got a quite nice pair of in-ear headphones which block noise very well (with a very tight seal, not noise cancellation). Before that, I used Apple earbuds.

With these better headphones, I'm now often hearing a hissing noise. This happens constantly while a sound is being played (music, alerts, etc.) and for several seconds after. I assume this was happening with my previous headphones but there wasn't a good enough seal for me to hear it.

This doesn't happen with my iPod or iPad. How can I stop it from happening?

Answer: 
Hope this helps some of you, what solved my issue was the following,

* Open Terminal
* type `cd /Library/Preferences/Audio` and press Enter type
* `ls` and press Enter you should see two files:

```
com.apple.audio.DeviceSettings.plist
com.apple.audio.SystemSettings.plist

```

* type `sudo rm com.apple.audio.DeviceSettings.plist` and press Enter it will prompt you for your password
* type `sudo rm com.apple.audio.SystemSettings.plist` and press Enter this will delete the audio settings for your OS
* type `sudo killall coreaudiod` and press Enter that will restart the audio system and all should be working now, at least, it did for me.
**UNPLUG THE CHARGING CABLE FROM YOUR POWER PORT!**

This may sound crazy, but as another User (DOM) has kindly suggested, (and was downvoted for,) this is a Grounding Problem with the Mac itself; not your wires, not the sample rate, not the bit-depth. 
**This solved my (annoying) noise problem.** However, I think it may have to do with *which* outlet I plug my MacBook Pro *in* to.

I'm connecting my secondary MacBook Pro (mid-2012) into a Monster Power PRO 2500 Rack Power Center for my studio desk. It's plugged into the front outlet. I'm thinking that's causing my problem. However, it *may* be caused by *any* outlet I plug into since I've yet to test any others.

*Anyone else try using different outlets?*