Well, yes and no, as it depends on how you have installed and wired your antenna, radio, etc. Trunk lip mounts are second only to mag mounts as the worse way to mount an antenna. I'm sure you haven't done any bonding, or other noise abatement procedures. In other words, there is more to it than throwing the rig into the car and driving off.
There isn't enough room here to explain it all. I suggest you look over my web site, especially the wiring, bonding, and antenna articles. Once you have tackled those, and you still have the problem, send me an e-mail.