When dealing with a flashing grey screen - it's typically indicative of tracking issues first and foremost.
When troubleshooting traking issues, you'll want to generate a SteamVR system report and search the output for reflections or other basestation specific lines.
The way to confirm a reflective issue would be to create a SteamVR system report, save the file, then open the file in a text editor and use Ctrl+F to search the document for the following term: back-facing.
If you see a high number of back-facing hits, it's almost certainly a reflective issue. Here's an example output that shows a clear-cut case of reflection-based interference:
Sun Jun 26 2016 23:02:09.676 - lighthouse: LHR-4R8EF209 H: Dropped 32312 back-facing hits, 2069 non-clustered hits during the previous tracking session
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