If the noise is gone, the hard drive is your problem. If the laptop makes clicking or grinding noises and you still have video on the screen, you can run a hard drive test utility.
Random connection dropping is another commonly observed issue, usually with a connection sustaining itself for anywhere from a few seconds to 10 minutes before dropping.If your laptop does not start at all or it starts but will not boot properly, it’s possible that you can fix the laptop at home without taking it to a repair center. I’m not sure if I can cover all situation at once, so I will update this post as more examples come into my mind. First of all in this situation check the AC adapter. If you cannot do that, find a known good AC adapter and use it for testing the laptop. You plug the AC adapter but the LEDs (power light, hard drive light, battery charge light, etc…) do not light up and the laptop will not react at all if you press on the power button.If you have to replace the AC adapter, make sure you use a correct one.The output voltage must be exactly the same as on the original adapter.Perhaps more troubling, some Mac users who had functioning wi-fi previously have discovered that new wireless difficulties have appeared on their Macs after updating to the OS X 10.10.2 release of Yosemite.These cases are likely outliers, as OS X 10.10.2 has resolved wi-fi difficulties for some users as well.Given the reliance on internet connectivity these days, that can be a very frustrating situation to experience and to troubleshoot.The very first thing you should do is add a new network location in OS X, set DNS manually, and then reboot the Mac.This resolves many network issues that Mac users experience with wi-fi and is an easy procedure: For sluggish Bluetooth related Wi-Fi problems, switching the router to 5GHz is often sufficient to resolve any trouble.Disabling Bluetooth entirely also resolves the wifi-bluetooth conflict, but whether or not that is acceptable will be dependent on each user and their respective hardware.