i have '97 sc300 hallowed cat been running wo cat for abt 5 months and it was fine, well taken care of. when i accelerate from 2000-4500 RPM and let go of a gas it makes the "bbbrrrrrrrrrrrrrrr" noise. WTF is it?? hooked up OBD-2 reader, shows- 2 oxy. sensors? but would the car even...