air commin out of dump valve during lift????

If i lay my car all the way out, and lift it, a lil bit of air comes out of the dump valve, not much, but enough to hear. It only does it if there is little or no pressure in the bag, say less then 15 psi. The suspension works just fine, no leaks, no problems, it just blows air out during lift. anybody know what causes it, or how to make it stop? And oh yeah, I got 1inch AIM valves, but come to find out, it did the same thing on my 3/8 SMCs.