Check Engine Light

I have a 2.2L 98 Sonoma. I replaced the battery last night. And now the check engine soon light is on constantly. I have noticed that for about the past 3 weeks the alternator seems to making noise could this be causing the light to come on. I had them test the system at the place where I bought the battery and they said my alt. was putting out the right voltage. Any advice would be appreciated.

Stop at autozone, they will pull the codes for free... But it is also possible that you bought a bad alternator with a bad regulator on it...