How to fix FPS drop after a period of time (EGPU)?

Question

Video cards

Using an EXP GDC eGPU with a GTX 670 connected to a 550W PSU. The eGPU adapter is connected to a Lenovo G780 laptop via miniPCIe.
In games (any) after 5-15 minutes of the game, FPS drops by 50% (feeling of switching to PCIe speed 1x mode) or the game crashes (less often) or the video card driver crashes (extremely rare).
* With such a "phenomenon" in the connected speakers, you can hear a signal of a short interference, similar to a power surge.
*Tested various latency modes on the eGPU board as well as in the BIOS. But maybe there's something I don't know.
*The video card was tested on a PC, no freezes or FPS loss were observed.
I post the GPU-Z logs at the end on 2015-05-09 16:46:24 you can see the drop point, with the game crashing. When the FPS drops, the frequency and voltage of the video card do not change.
Link to the GPU-Z log
!If you minimize the game for 1 minute after the FPS drops, it will recover to the highest value before the crash.
!If you start the video player in the background (pause), then the video driver crashes will stop, a well-known way to bypass such problems.