This number keeps calling.

Out of curiosity I answered the call. There was dead silence, an odd sound from someone's voice (like "gah"), and then . . . NOTHING. Does anyone know who or what this is?

I suspect this number isn't even valid, 312 area code is legit but the 800 prefix is likely made up. Scammers do this all the time, heck I've even been called by someone using my own number as ID. I just flat don't answer calls anymore unless I know who they are and I definitely don't return calls unless some at least leaves a message.

Called and claimed to be a part of Nicor.  Did not ask for me personally, but asked if I was the person whose name was on the bill..... Said they were trying to discount my bill.....seemed like it could be a scam, but was not sure.  Told them I was not interested just to be safe.

I just got a call from this number. I said hello, no one said anything. Then a voice on the other side of the line started saying "hello? hello?" in an annoyed tone. Then, in a rather aggressive manner, they said needed to talk to the person who gets a Nicor bill. I said I don't get one and they said "you don't?" in disbelief. I said I don't because I don't even live in a state served by Nicor. The caller then abruptly hung up. Totally unlike any other customer service calls I've had. Seems like someone calling to scam me!