Was this a rattlesnake or a bullsnake (read)?

I was at the wapsi river in Iowa near the quad cities, and I was walking in the woods beside the river and o saw a snak and it was rattleing it's rattle like CRAZY from what I could see the rattle was brown, I was too scared to check if it was a rattlesnake or bullsnake and I ran back to my dad an he said it was probably a bullsnake but do bullsnakes have rattles and are their rattles brown? So do you think it was a rattlesnake or bullsnake?? Please help --Brittany