Volvo - XC90 :: 2004 - Thump In Front End Followed By A Very Brief Internal Power Failure

My 2004 Volvo XC 90 has a severe "thump" in the front end, which is then followed by a very brief (split second) internal (meaning dashboard lights, hi-fi, dome lights, etc) power failure. Initially, the power failure would last only a split second and then car would continue running as normal, and there we no error codes or check engine lights.

But on the last long drive home, the "thump" was harder than usual, and the lights internally completely went out, hazard lights could not be turned on, blinkers could not be switched on, hi-fi went out, etc (though the electric windows would work). I pulled over, and turned the car off and restarted it, and the yellow exclamation point dashboard icon/alert lit up, and a service message flashed referring to the anti-lock brake failure, and that the SRS needed to be checked.

This problem has been occurring for a couple of months, and is very intermittent. Before this last incident, I took it into the dealership, who could not figure it out,. Now that I have an error code, I have it at another dealership, who seems equally mystified and have told me that they don't think the error code of check the SRS is going to fix the problem. The engine thump, followed by electrical failure seems really weird....