We had that on our street a few years back with the added benefit of houser alarms registering a jamming attempt and activating in a 30+m radius. The culprit was traced to a duff Toyota keyfob. The owner gave the keys to his toddler to play with, the kid was teething, bit on the fob and some spit permanently shorted the ON button. Apparently there was no delay and no protection in the Toyota fob design. You short the ON and it is ON - all the time transmitting at max rate. Perfect DIY jammer.
So it is not necessarily a jammer. A mummy with a toddler driving a Toyota is equally possible.