1st off, the oil light is a dummy light, it only comes on when the oil pressure is REALLY Low, just because you have oil doesnt mean that you have good oil pressure, thats what the light is telling you, its not telling you that you are out of oil.. with that said, what kind of vibration is it, is it in the steering wheel? does it feel like the motor is vibrating really bad, does it get worse with higher RPM's/Speeds?? If you have low oil pressure then your parts arn't getting lubed right and that will cause the motor to vibrate.. About a year after buying my 99 SI (new) I started to hear/feel a clicking/knocking when I turned, For quite some time I thought It was a CV joint(didnt know any better at the time), then it started to knock without turning the wheel, as soon as it did that I knew it was a bearing failing on me, I had No money at the time, and drove it for about 2 days(very easy) B4 I spun a rod bearing and shot a rod out the side of my block.. Give us a little more info about the sound, where it sounds like its comming from(left? right? rear? front?) And let us know if you can feel any of the vibrations on any parts like the shifter/brake pedal, steering wheel, and such