Recently I noticed I am getting a lot of static on the radio only on AM its more at times the static begins as soon as I turn the key on the 2nd position and continues there after. At times its more and if I am driving under even a small bridge. I checked the alternator the charging is fine since that was the last electrical equipment that was replaced about 4 months ago. I used commercial rust remover to remove any rust off the grounding points but it dosent help. anyone has any more suggestions? or things I could check?

Thanks for your help.