Laptop suddenly reboots mid-game but not in stress-tests?

Note : My laptop is using a desktop GPU and PSU with an external GPU adapter. The GPU is not a discreet , built-in one.

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Symptoms :

Laptop suddenly reboots in the middle of playing Watch Dogs.External display goes "No Signal" , my earphones give me a horrible crackling noise and the laptop display (BIOS uses the integrated Intel HD) goes "Windows Did Not Shut Down Successfully".

Happens in 20-30 minutes into the game but not during heated moments; other times runs for hours no problem.

Similar issues found here and here .

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What I’ve tried and ruled out :

• Disabled any "Turn Off Display After" settings.

• Sucessfully ran overnight for defragging ; no problems with the power button and cables. At this time, it was running from integrated Intel HD.

• MemTest64 found no errors with memory or CPU.

• MSI Kumbostor’s "(GL) MSI-01" ruled out GPU or PSU problems.

• The battery icon says " Plugged in, not charging " but it looses no charge, this is not the problem.

• I briefly posted an answer that the cause was earphones. But after thorough testing I can see that it crashes regardless.

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Setup :

• Laptop: Panasonic Toughbook CF-53 (specifically, CF-53SAPZYC7) with cleanly-installed Windows 7 Pro SP1 64-bit (latest updates and drivers AFAIK)
• CPU: i5-3340M
• RAM: 8GB DDR3 , dual channel
• eGPU adapter : EXP GDC Beast v8 Mini PCI-E
• GPU: GTX 750 ZT-70704-10M ; Driver 460.79 (latest)
• PSU: Zebronics 450 W PSU (ZEB-N450W)
• No overclocking whatsoever

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EDITS :

Testing if interference from other devices was the case, by securely wrapping all cables from the exp gdc in aluminium foil. Seems to be promising. At least all glitches and stutters are gone.