2006 pontiac g6 engine noise

I have a 2006 Pontiac g6 with a loud clicking noise in the motor. It sounds like the noise is in the top and I currently have the motor taken apart at the valve covers. I was told it was probably a lifter but I cannot find any lifters. There are pushrods and I have taken them out but really don't know what I'm looking for. The motor is a 3500 v6. Any help would be greatly appreciated.