I've been trying to research this issue with little result for BMWs. On my '08 X5 I use the aux input for my iPhone with power coming from the inside armrest cigarette lighter via a usb power plug. The iPhone is using a line out cable that splits the audio to a standard headphone plug and the power is coming from the usb end. I get a lot of engine whine/noise that can be pretty annoying when listening to softer music, especially when at higher speeds on the highway. I haven't found much info specifically for the X5, but other brands have had similar issues. Is the only answer something like an in-line noise suppressor?

usb power plug:
http://www.amazon.com/gp/product/B00...ls_o00_s00_i00

noise suppressor:
Amazon.com: Pyramid NS12 12 Amp InLine Noise Suppressor: Count Bishops: DependableResource

Any input or advice would be greatly appreciated.