Without knowing any details about the substrate it's hard to say that this "shouldn't be an issue". Ask your rep for a media guide, it is very detailed and should help point you in the direction of whether it's a substrate or a machine issue. All the above recommendations were solid so do all of those as well, and I have one other thing to try if you still see marks.
For purposes of this description I'll assume it's not a substrate issue and that all the aformentioned adjustments haven't helped. One other adjustment that may help is changing the compression switch on the fusers. Each fuser has a 3 step (I beleive both are 3, the second fuser may be a 2 step) hard switch to adjust compression. Once you have the media guide, there will be a matrix in there that will give you the exact compression combinations by substrate, but once you get up to a decent weight they will both be set on the "Release" position, so this may help to see if it alleviates the indents you're speaking about. The switch can be found on the outside of the assembly on the left side looking at the machine. If you don't see it immediatley, open the jam clearance area on the fuser to expose the nip belts you will see it directly on the face of the component that hinges, but you can access it while it is closed. Each position is marked by 1 dot, 2 dots, or 3 dots and the more dots, the lower the compression - so both switches set to the position with the most dots will be the release position. Set both to the Release position and see if this alleviates the issue. If not send me a PM and provide more detail about the substrate and the exact indent marks (position on the page, shape, consistency, etc) and I can do some investigating.
