I have a 2004 dodge durango, hemi, awd. when i shut the truck off, i can hear a buzzing sound coming from somewhere under the truck for up to a minute. if i crack the gas cap during this, the gas tank sucks in a bunch of air and the buzzing noise stops. any insight for me. I'm good with engines and fix my vehicles myself, but this ones got me stuck. also, today my wife was out around town and the engine light came on and the engine shut off. she was able to restart it right away. I checked the codes when she got home and had p0172 & p0175. basically "running rich" right? what should i start checking?

Thanks, Behn