Your description claries things somewhat. I can now understand how the flasher and unknown sound could occur in synchronization.

According to the Volvo drawings, the purge valve is located in the rear, near the fuel tank, so it is possible that the sound (of the valve operating) could appear to come from below and to the rear. It is operated by the engine comtrol computer, which is located in the engine bay. The Volvo drawing does not show a connector in the purge valve wires, but it is possible on was added for diagnostic purposes. While I cannot be 100% sure that the wires you described connect to that valve, it is the only component I can find that matches both the number of wires (2) and wire colors (Bl/R and Bl/W).

It is possible that the ECU detected, and has stored, a suspected component fault. It may clear itself after 50 (or so) operations of the ignition without a repeat of the fault condition. Otherwise, you may need access to a "scan tool" to clear (turn off) the lamp. I assume the car seems to be running OK. You might also check of your fuses visually; your temporary connection may have caused one to blow.