Radio Static 740I

I lease a 2001 740I. I get lots of breif bursts of Radio static (high pitched whine) on AM band whenever I go under a bridge or underpasss. Also occurs near utility lines. Very annoying when traveling on I-95 as I go under one underpass after another. Dealer has improved insulation on radio wires near GPS system but not much improvement. FM band not affected. Weak AM stations exagerate static.
Any ideas would be most welcome!

Thank you.