Bought a used '09 C300 a month ago and now I notice a high pitched hum at around 40 mph. The sound is not loud and so I didn't notice as the sales guy and I were yakking during the test drive. It goes away when I let off on the gas hence I'm wondering some kind of transaxle(?) issue or bearing issue.
If I go to dealer he'll say it's wind noise but I think not. Car has 64K on it and I have a 3 year CPO deal on it when I bought the car in 12/14.
Thoughts?
And lastly is there any way to play music from my Iphone6 via the cars sound system through some aftermarket mod? Car does not have nav or upgraded stereo.

 

I would take it to a dealer and get them looking into the whine at speed. You have a warranty so you shouldn't have to be concerned about the cost of the repairs.