HHonors Parking Discount

A couple of years ago, when I was still silver, I was at the Hilton in Downtown Cincinnati and parked my car overnight. When I checked out and got my bill, they had knocked something like $3 per night off of the parking rate, and I was told this was because of my Hilton Honors membership.
Has anyone encountered anything like this elsewhere?
I'm going to be going to Chicago in a couple of weeks, and would love to stay somewhere with a ~$20 overnight rate, but am not prepared to pay quite that much.

Thanks!