I have a 2000 Jetta VR6 that develops a humming sound that eventually becomes a vibration in the brake pedal. It only happens when the outside temperature appoaches 90 degrees. When I turn the A/C off it goes away. It doesn't matter if the car is moving or standing still. The only code that is showing up is P0411 Secondary air system. Anyone had this problem? Sorry if it's in the archives but search isn't working and it's starting to bother me.

Thanks in advance for any help.

2001 Desert Green 225 TT Coupe, Canton, CT, No mods to date.