Weird Noise with CEL on- 1997 Camry 4cilinder LE
 

Hi guys, this is my first time posting so please forgive me in advance if someone had already answered my questions in another thread.

Symptoms:
One week ago, my engine light turned on spontaneously while the car was on idle. I noticed a strange noise (sounded like rustling leaves through a pipe) whenever I stepped on the gas pedal (only when reaching around 4000 rpm). The sound came only from the driver side, and appears to be right behind the gas pedal and within the dash. It disappeared when I am driving and reappeared only when I am idle and revving up the engine.

Repair and Car history:
1) A week prior to this incident I changed my radiator, thermostat, and had the mechanic try to flush out the heater core because my heater doesn't work. It didn't work and they told me I had to replace the heater core. It was too much money at the time so I didn't change it. When they closed the hood, there were antifreeze all over the interior of the car and they washed it down with water.
2) A couple of days later, I filled up my tank at a BP nearby my house but I suspect the gas was bad due to the fact that the overhead light at my fill up station keeps flickering. I didn't screw my gas cap that tight.

Self Check:
1) I researched online and they said a loose gas cap can cause the engine light to be on. I tightened it all the way and its already been one week, the light is still on.
2) My antifreeze reservoir is full. Nothing seems to be leaking under the hood. I did notice the radiator fan didn't spin when the car was on. Any significance?

So my ultimate questions are: What can be causing the "leave rustling" noise?; What is the cause of the Engine Light? <----I know the answer can be "anything" but I would just like your opinions due to what the information I provided; and Is there anything I can do myself to check for the solution?

Thanks in advance guys!

1. pull ECM fuse out for at least 15 minutes. better overnight. this will reset all codes stored in ECM. see what follows.
2. 4000 rpms? what are you, racing her or something?
3. I'd love to HEAR the noise. so far, wild guess is - rockers noise due to sticky lifters, or timing too advanced. Pour can of Seafoam into crankcase and see what happens. safe to drive on. OIL CHANGE sometimes does miracle cure to noises.

Fastest troubleshooting method is to get the codes read.