Your first course of action should be to move up and down a few channels on your receiver, to make sure that you aren't on an adjacent channel.
Next, make sure that all of your antennas are screwed in fully, and make sure you don't power up the video transmitter without an antenna attached. Doing this will damage the transmitter.
Make sure that the antennas are pointing directly up. Cloverleaf/ Skew Planar Wheel antennas have a deadspot directly above them, and so you want to position them so that they are radiating to the sides. (Imagine having a donut, and the antenna goes in the middle of the donut. The donut is your radiation pattern. There are weak spots above and below the antenna, so you want to make sure you're not receiving in the antenna's weak spot.
Finally, try it in a different area. RF noise can be particularly high in one location, and virtually nonexistent in another. Testing your gear in a variety of locations gives you a good chance of finding a place where RF interference is minimal.