At 40MPH , the 'growl' is present? If so , keep same vehicle speed and downshift trans , if the 'growl' stays consistent it's not the engine , most likely.If noise changes with engine speed , then need to have a mechanic there listen to it , first-hand.
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Do you hear this noise with the engine running and car parked? If the only time you hear it is when moving it aint the motor.
Most likely wheel bearing noise.
Maybe the noise is screaming Redskins fans!.............never mind.......
Right back in the picture. I love it!