I have tried all the pin mode combinations on A4 & A5 with no success.
pinMode() does not affect the analog nature of the pins.
pinMode() has no affect on the digital nature of the pins when you use them for I2C.
Going to sleep does not necessarily disable the A2D converter.
Going to sleep does not necessarily disable the I2C hardware.
You posted in the Programming section, where one of the requirements is to POST YOUR CODE. Why haven't you? Why should anyone try to help you when YOU can't follow simple rules?