Me, never

Seriously, im not rite up on the fezzi turbo fuel systems but most EFI systems have some sort of pulsation damper in the fuel line to smooth out the pulses in the fuel caused by the injectors opening and closing, you havent removed or changed anything like that have you?

Have you moved the fuel line in any way, is it catching on something and transmitting vibration?

Have you altered the fuel pressure or changed the regulator, pump, injectors or anything on the fuel system?

Bit of a difficult one without actully hearing the noise to be honest.