[Gnawrocki1]

Still working my way through the air systems. I'm hearing this sound (in the video) from the air tank in front of the passenger drive axle. Does anyone know what it is? My suspicion is it's letting air out, but I would like to really know.

Having trouble posting a video, but the sound is occasional pinging. It lasts for a second and happens every 10 seconds or so.

I am going to guess the sound is air flowing past the check valve that is mounted right next to the tank.  I had that issue and replaced the check valve.  The sound went away for about a year, but every now and again I hear it again.