First of all, what new supercharger mod? Pulley? Something else? A smaller pulley may make you more sensitive to octane. If you're getting KR (and only a scantool can tell you as in the previous reply), you have to combat it by finding cooler air and/or higher octane fuel. Mine runs only on 92 minimum now.
Your SES light will not be about KR. It doesn't set a light. I'd suspect with a rattle like that that your CAT is shot, killing your performance and making you run hot. And again, that'* not your SES light.
You can use the 'flash feature' to extract your own codes. Do it, and get back to us.
Ultimately, you need to get a scantool on the car to diagnose it, as Gordy stated.
Moving this to 92-99 for you......I don't think it has anything to do with your supercharger.
(if you put your location in your profile, we can find out if someone has a scantool near you)