I stopped using the foam things, because i never felt or heard the difference, btw. Which confuses me. I actually try to keep slack hose inside the frame to make disassembly easier, so i dont think my hoses are so tight inside that they can't move.
Maybe i'm just lucky.
Maybe if you dont use the foam, you'd have to be unlucky to hear a rattle?
If you route 4 hoses, dont use foam, it will make you want to end yourself. Dont ask me how i know.
It's funny that our experiences differ like that.
It might actually be the "slack hose" in the frame that keeps it from rattling around. Sounds counter-intuitive first but think about it:
1) if you cut it to length (i.e. no extra slack) the hose will take the shortest route through the down tube, so probably in a somewhat diagonal fashion. That means it won't sit tight against the walls but kinda floating in the air. It won't be that tight either that it won't move at all as you cannot pull it that tight. So once you start riding and hit some bumps, your "floating" hoses will start hitting the walls aka rattling ensues.
2) If you push in some slack hose, you will push it against the walls of the down tube, as it squishes in there somehow. That might actually hold it in place much better than the "cut to size" variant from option 1. Since it is pushed against the walls it cannot move as much as the floating hoses and therefore won't rattle as much (or at all depending on how squished it is).
Since I didn't want to take the chances and only have one brake hose running through it (electronic shifting), I just used some foam and be done with it. Would have hated to open the system up again after bleeding the brakes and all.
