Engine Performance problem
1996 GMC Jimmy 6 cyl Four Wheel Drive Automatic 122223 miles
About 10 days ago my check engine light came on. I have recently had my oil pressure switch replaced due to a massive oil leak and about 9 months ago I had 6 spark plugs, the dis cap and rotor, a set of plug wires, and the fuel filter replaced after the dis rotor was found burnt and off of the distributor. When I turn the car on, I can hear a faint but high pitched sound, kind of like a whistle. Also, there have been a couple times when I have turned the car off and faintly smelled something reminiscent of burning rubber (both times I had been driving for over 30 minutes.) The car seems to be running smoothly however and I all of the gages read normal. I am a college student and not particularly keen on auto knowledge so I was just wondering what the problem could be and if it was something I could fix myself so I didn't have to spend an arm and a leg, thanks.