It could be condensation, if you loosen the screw at the bottom of the water trap container on the compressor when the airbrush is being used, it should spit out the water. Then tighten it up again. I use an Iwata so if may be different if you have another type.
Hope this helps and that I explained ok.
luv Sarah x
My airbrush gun seems to spit out paint. There doesn't seem to be a clog or block has anyone got any idea what the problem might be?