Since your fixing this now, it's a great time to pull the battery and tray and check under there. My car is 99% rust free (under coated thank God) and my towers are clean/spotless. When I was fixing some bad aftermarket wiring I pulled the battery tray for more working room only to be greeted with a rusty surprise. It was simple to wire wheel off and paint back. Had I not pulled that tray it would have just kept getting worse and worse and became a problem vs a minor irritation.
Good luck and listen to these guys advice, they've been there and done that.