Batboard

This question may be better on the general forum, but here goes, I have a 2004 explorer with an A7 UHF Spectra, I have been getting a lot of interference when scanning, almost sounds like a machine gun, but not all the time. I was using an A/S 5db gain Mosaic antenna on the center of the roof. I switched to an old standby 1/4 wave stick and I have not got the noise as yet. Has anyone else run into this?
Thanks