Check Engine Light

I have got two questions, the first is my check engine light recently came on and never went off and I have been reading online ways that you can see what code the the computer is giving out by two ways, the first is turn the key on/off/on/off/on/off then leaving the key in the on position and it suppose to give the code which I tried and did not work, the second is hold in on the odometer/trip reset button and turn the key in the on position for a few seconds which I tried and it does make the instrument cluster check but does not give the code after it checks the function of the gauges. Is there any other way I can check to see what code my truck is giving.

The second question is that there is a loud whistle noise in my truck when I am just feathering the gas, maybe a vacuum leak I don't know but I would like to know if there is any advice that I can get to try to figure it out before I bring it to a mechanic.