90% chance it's the 12v battery. Many Volts sat for a long time before being sold, long enough to let the 12v battery drain too low to fully recover.
7.5% chance it's a poorly-connected ground.
2.5% chance there's an aftermarket accessory causing a ground loop or electrical interference.
2013 Volt, Silver Topaz, leather, Bose, SP 1, SHVCS Defeat Plug,
Morimoto 35w 4.3k HIDs, Damplifier/Dynaliner, ERDTT switch, EVExtend 1500W Inverter.
CS mode: 43.5 mpg @ 65 mph. Best EV Range: 57 miles on 8/10/13.
2006 Mazda RX-8, Fast & Furious, rotary engine, 7.9 mpg (racetrack).