To keep a long, shocking story short, I just got zapped by touching the steel bracket holding our garage door opener and the top of my DC. Further investigation shows that the DC is properly grounded, and the voltage is live between the garage door opener and any ground, such as an exposed steel conduit. Obviously, this is not a good thing. It stings.
The garage door opener is plugged into a 3-prong outlet. My first step will be to verify that outlet is actually grounded. What else do I need to be looking for?