Q: When i slow down my GMC Envoy shuts off and makes a humming noise like a toy car, told to replace the engine, noise is still there

If the humming noise occurs when the car is stationary with the engine on at any RPM, then it is engine or transmission related but the noise could originate from an accessory drive on the engine. However, if the noise only occurs once the car is moving, then the origin of the noise is more likely to be a wheel bearing. Stalling is typically not due to mechanical problems within the engine. The more likely causes are a faulty mass airflow sensor, faulty camshaft or crankshaft position sensors, worn spark plugs, wires or defective ignition coil(s), inadequate fuel delivery or pressure (clogged fuel filter, injectors, faulty fuel pump or pump circuit), contaminated or old gasoline, defective throttle position sensor, faulty idle air control valve, leaks in the EGR system, intake vacuum leaks, and so forth. Typically, the issue is limited and fairly easy to resolve. If you request an engine stalling diagnostic the responding certified mechanic will get this resolved for you promptly and the mechanic will also deal with the noise issue you have mentioned. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.