Humming Noise

It may be an exhaust rattle, but without hearing and locating the noise in person it is very difficult to know for sure. Can you determine where the noise is coming from?

My STS makes a humming noise too, It stops when the rpm's get over 2000. I found out it's the alternator. Labor alone is over $350. Cadillac wants over $700 for the part! What a joke! Auto Zone has a remanufactured part for $275 plus $50 core charge! Bruce J Chandler, AZ

it could most likely be that your low on power steering fluid. the reason it would subside when you accelerate is because the engine is pushing the power steering fluid through the system faster.