Strange issue with external monitor, only working when external speakers plugged in (using Thunderbolt to VGA adaptor)

Hey – I am having a very strange issue with my external monitor; where it only works if my external speakers are plugged in and connected.
I am using a late 2011 Macbook pro, running Mavericks 10.9.4, along with an MBox 2 (USB Audio Interface), and two powered speakers (KRK Rokit 5). This setup has had no issues. I have just acquired an external monitor (Benq T2200HD), which I am using with a thunderbolt to VGA adaptor (a cheap Chinese knockoff adaptor).
To start - I plugged the monitor in with the thunderbolt adaptor, and it powers up and works fine. However, there is a nasty buzz coming from the speakers. I did some research and it looks like a simple ground loop issue. I did a bit of troubleshooting, and this is where things get weird.
What I found is - If I unplug the MBox, the monitor loses signal from the computer (displaying ‘No Signal Detected!’). Further, if I keep the MBox plugged in, however unplug both the cables from the MBox to the speakers, the monitor loses signal. It doesn’t matter if the speakers are turned off, however they need to be plugged in (or the monitor loses signal). Weirder still, I can unplug the MBox, however the monitor will work if I plug in the speakers through my macs headphone jack.
Simply put, the monitor only works if there is a direct connection between the computer, the speakers, and the power source.  What is going on here? Is the monitor grounding through the computer port, to the speakers (I don’t know how this works, is this possible?). Could it somehow be the cheap VGA adaptor I am using?
Some other information:
- Everything is plugged into the same multi-box for power. I have tried plugging things into separate sources, and the result is the same.
- If I unplug the thunderbolt adaptor, then the speaker noise disappears straight away.
- The ground noise doesn’t appear in my headphones, which are plugged into the MBox.
Any information would be great – am I missing something here, or is this genuinely weird?

Well, I went back into Best Buy to test on 3 other laptops (2 Asus, and their floor model for this Sony). It seems to be doing the same problem so at least I was able to rule out broken hardware issue on my particular laptop.
Here's what I did to test:
Since I couldn't really install Adobe Premiere on their machines, I used the DVIO software (http://www.carr-engineering.com/dvio.htm) and a 5 min clip I captured.  I transferred onto their machines, hooked up my Sony D8, and attempted to play the video.  It would play for 15 seconds and then stop and jitter with a loud noise (like it does on my laptop).  I even tried changing each machine's firewire driver to the legacy one and same results.  I pulled a brand new 4 pin to 4 pin firewire cable off their shelf and still the same problem.
I think I've nailed it down to Win7x64 bit Home Edition not playing nice with Firewire driver.  Very annoying.  I can't find any concrete evidence of this from other users on any of the forums that have my particular problem, but from my own testing, it's all I can conclude.
I have 2 other things I can try:
1.  Opening the laptop and looking at the firewire to maybe find appropriate driver (ugh, I don't want to have to open this thing up).
2.  Upgrading to Win7x64bit Pro and possibly testing with XP on the new MS Virtual PC (http://www.microsoft.com/windows/virtual-pc/).  I can't do it with my Home edition apparantly.
Who needs to view video on an external TV anyways....sheeesh...(scarcasm).
Tim

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    Hey – I am having a very strange issue with my external monitor; where it only works if my external speakers are plugged in and connected.
    I am using a late 2011 Macbook pro, running Mavericks 10.9.4, along with an MBox 2 (USB Audio Interface), and two powered speakers (KRK Rokit 5). This setup has had no issues. I have just acquired an external monitor (Benq T2200HD), which I am using with a thunderbolt to VGA adaptor (a cheap non-apple adaptor).
    To start - I plugged the monitor in with the thunderbolt adaptor, and it powers up and works fine. However, there is a nasty buzz coming from the speakers. I did some research and it looks like a simple ground loop issue. I did a bit of troubleshooting, and this is where things get weird.
    What I found is - If I unplug the MBox, the monitor loses signal from the computer (displaying ‘No Signal Detected!’). Further, if I keep the MBox plugged in, however unplug both the cables from the MBox to the speakers, the monitor loses signal. It doesn’t matter if the speakers are turned off, however they need to be plugged in (or the monitor loses signal). Weirder still, I can unplug the MBox, however the monitor will work if I plug in the speakers through my macs headphone jack.
    Simply put, the monitor only works if there is a direct connection between the computer, the speakers, and the power source.  What is going on here? Is the monitor grounding through the computer port, to the speakers (I don’t know how this works, is this possible?). Could it somehow be the cheap VGA adaptor I am using?
    Some other information:
    - Everything is plugged into the same multi-box for power. I have tried plugging things into separate sources, and the result is the same.
    - If I unplug the thunderbolt adaptor, then the speaker noise disappears straight away.
    - The ground noise doesn’t appear in my headphones, which are plugged into the MBox.
    Any information would be great – am I missing something here, or is this genuinely weird?

    Hello cgoldberg11
    Please go to the below link to test if you are having a speaker hardware failure.
    Testing for Hardware Failures (Windows 7)
    This will rule out hardware failure, let me know how that goes.
    Thanks
    If I have solved your issue, please feel free to provide kudos and make sure you mark this thread as solution provided!
    Although I work for HP, my posts and replies are my own opinion and not those of HP. .....
    Reguards,
    Mo

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