I need to do this on my car. My dad found a TSB for it, but I've never done anything about it in the year and half I've had it. It gives a somewhat annoying resonance at about 2k RPM. Must not be annoying enough for me to have not done anything yet, lol.I'd look at the brake lines and fuel rails. There is very little clearance between these lines and the firewall and we have had multiple reports of them rattling against the firewall between 2000 and 2500 RPM. The solution is very simply pulling them away from the firewall by about an eight of an inch.