strange noise using skype on mac book pro

Using a monitor with a mic included? Many modern monitors have mics, and it’s possible your app or computer are defaulting to that mic rather than your Mac’s internal microphone. If you recently downloaded an app that requires permission to use your mic, it could be causing issues that prevent the mic from working at all. A Mac or MacBook microphone not working can be caused by apps. This is a good time to return or repair your Mac. Though all Macs go through quality checks, sometimes things are just broken. If you recently purchased your Mac, it’s possible the mic is just broken. There could be several reasons for a Mac or MacBook mic not working. Believe me - try it! If it doesn't help then make sure that you have a replacement IEC power cable (the one that has a female 3-pronged end and a male 3-pronged end) to swap out to if not successful.Reasons why Mac’s Microphone stopped working As a professional I cannot profess to know that the possible negative implications might be from having a non-grounded iMac but let me just say that this is not the first time that I have done this with a computer or any type of gear for that matter to just basically 'move on'.They did/would not offer this solution but for me, after working in recording studios for more than 25 years now and experiencing MANY types of grounding issues with regard to BUZZ in the audio signal - it led me to just rip that ground plug off and move forward. Apple's mention of a 'ground loop' possibly being the problem in other posts was the best advice I found. Plugged it back in, booted back up and SOLVED. I shut down the iMac, unplugged the power cable from the wall, grabbed a pair of needle nose pliers and then ripped off the GROUND PLUG from the power cable.

all weird, misguided and did not solve the problem. Read and tried a few things that were completely useless and weird to even give a try (but I did regardless) - things like : 'zap the PRAM'. : something like a system sound would play, there would be silence, and then after about 10 seconds or so the BUZZ would constantly output. I use the headphone jack output for audio playback from my iMac (Pro Tools, iTunes, etc) and after upgrading to the iMac from my Mac Pro (early 2008, quad core) physically configured the same way (headphone jack output to my speakers) the iMac would constantly emit a BUZZ shortly after any sound was outputted from it. Well, Apple probably won't like this advice but it EASILY worked for me :

Strange noise using skype on mac book pro