Two days ago, my sister to the 8 to school and left the lights on. So the battery is dead when she comes back and I have to go give her a jump.

I haven't driven the car in a while so I took it back home and put in some more motor oil and engine coolant.

Immediately after, I went to go fill up the gas to half-a-tank and there were no lights.

However, the engine did sound different than I remembered. It sounds like a grinding noise (sort of like how those super-charged rx8s sound).

Today, I take it out again and I get the light. I checked the oil cap and it is on fine.
WHen the engine is in a higher rpm, it still feels as if it sounds different.

Spark plugs haven't been changed yet. I am hitting nearly 27k miles.

 

Did you check the oil dip stick before adding oil? and since you have 27k on the car, i think it is time for new spark plugs and igntion coils.

 

Yes, the oil reached the first line so I def. needed to add some.

 

Check your gas cap. The gas cap can set off your CEL. But i would get your car scanned so you know what the CEL is. Some auto parts stores like auto zone or advance auto parts will check the car for free. But since you are having problems in the high rpms i would suggest getting new coils and plugs or BHR ignition uprgade. Its a very nice upgrade. The oem setup is weak and often fail but the BHR kit is going to last