Q: P04042. In 328i bmw. 2009 how can a fixed

P0402 means the exhaust gas recirculation (EGR) valve is flowing too much recirculated exhaust gas when it is commanded to open the flow of exhaust gas into the intake manifold. A consequence is the engine could be running rough if the valve is stuck open and/or the engine EGR system may have exhaust leaks at the back pressure transducer. The noise you are hearing may or may not be related to this issue (i.e., the noise could be due to another issue). Depending on the results of the diagnostic, possible resolutions of this code are: replacing a stuck open EGR valve; replacing a broken catalyst in the exhaust; replacing an EGR temperature sensor or cleaning the carbon off of it to repair it if it registers too much of a temperature change; and replacing the EGR back pressure control valve. In your circumstance, if you request an EGR system inspection and diagnostic the responding certified mechanic will get this taken care of for you, including identifying the origin of the noise that you have referred to. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.