MacBook – Mid 2012 Macbook Air Black Screen

1) The region you are referring to is exactly where the fan is located. This may be what is causing the noise, although it could potentially be the optical drive as well. You can find an extensive DIY guide, along with the needed components, at iFixit. See below:

2) You will void any warranty you have with Apple, whether it be Apple's one year limited warranty or its extended warranty (Apple Care). Additionally, Apple may refuse to service it in the event that you fail to fix the problem.

3) Yes.

4) If you are okay with (2), and are able to carefully follow the guide linked to in (1), then yes. It's very possible that either the fan is damaged or there is some small component stuck in its vicinity, rattling around. It's also possible the optical drive is damaged and would require replacement. I wouldn't advise this if you were in any warranty window, but you aren't. Make sure to have the proper screwdriver if you decide to do so.

Best of luck

One place to start is testing your Startup/Login items, as it's likely to be something that's getting loaded during normal startup (e.g. a Startup/Login item, a font you've installed, etc) that's causing the problem.

So I would:

1. Startup normally
2. Go to System Preferences > Users & Groups
3. Select the Login Items tab
4. Take a note of your Login Items
5. Now remove all of them by highlighting them and clicking on the - button below
6. Restart your computer

Now your Mac will boot up without those login items loading. Test this and see if the problem persists.

• If the problem does persist, I'd then remove any fonts you've installed yourself.
• If the problem goes away you know one (or more) of the Login items were causing the problem. You can then go back and add them back one by one until you've identified the culprit.

Let me know how you go.

[EDIT]

I forgot to answer your question about what the difference is between booting into Safe Mode and booting normally. In a nutshell, booting into Safe Mode:

• doesn't load Login Items and any custom fonts you've installed (which is what my answer above is based on)
• ensures that only macOS kernel extensions are loaded
• runs a number of additional checks during startup (e.g. verifying/repairing your drive's directory, etc)
• deletes various caches

The last two can result in your system effectively repairing itself if your problems are related to corrupted caches or directory issues. In your case, since the problems didn't go away after previously booting into Safe Mode, the problem is most likely related to Login Items or 3rd party kernel extensions.