While going down the road, both air gauges start slowly dropping, then starts making a whistle noise, goes down to just above 90 , and the noise stops and the gauge goes back up to 120. It also did this in the parking area so I came to stop and when pull yellow truck button, noise immediately stops, red makes no difference. Any ideas what is going on here? The boss says put alcohol or dryer in it(He doesn't want to spend money on these things unless he has to). Where put?? I prefer southern comfort but that's probably not good for the truck. Thanks.