If it's the truck, the driver is an most likley an idiot. Most newer trucks are set so if the idle for xx amount of time they shut off. The bypass is to turn on the cruise and bump up the RPMs. If it's a APU, which is used for power, heat, AC ect in the truck they are pretty quiet, and shouldn't hear it. If it's a refer trailer.. well... nothing can be done about that.
In bed, according to prophesy.