Hyundai Repair: check engine light/a huming sound when I drive, secondary ignition, gaskit

Question
I have a 2003 hundai elantra gls with a little over 84000 miles on it I just had had the head gaskit and everything with the head done along with the timing belt water pump and thurmistate and spark plugs replaced I have a check engine light on and there test thing shows the code for spark plugs but the check engine light keeps coming back on also I have a humming sound that is prety loud but disapears when I turn left I'm not sure whats left to replace to fix my car

Answer
In regard to your humming noise, you should suspect that the brake pads are worn to the point where the wear indicators are rubbing or that the left front hub bearing is worn.

The check engine lamp will be a little trickier.  There is no specific code for spark plugs, so I presume you're referring to a misfire code (P030x where x is a digit (0-4) representing the misfiring cylinder or 0 for multiple or random misfires.  

Ordinarily, when diagnosing a misfire, I'd send you to the secondary ignition system, but the work that was done to the vehicle leads me to believe there may be other issues.  Since that's the case, I'd like to get a better understanding as to what is and has been happening with your car.

1.  Why did you have all this work done?  I.e., what was wrong with the car or what occurred with the car that led up to this work?

2.  What does "everything with the head done" include?  Was the head replaced?  Was it machined?

3.  What are the actual trouble codes?  If I know the actual trouble codes, that will tell me what sort of problem the computer has seen.  At present I'm relying on my interpretation of what you're telling me was told to you by someone who says the code is for a part that was already replaced.