if you position the centre support carefully, and cable tie the tubes to it, you can adjust the length of tubes to remove to much slack at the lhs. I then put some transparent plastic sheet under the tubes between the centre and cis, - simply taped to the top of the case - to stop the tubes dropping onto the heads at the rhs. The lid is raised about 3/8 inch at the front, resting on a couple of rubber pads - to let the tubes exit at rhs. My cis came with a modified cartridge cover, which held the tubes down at the print head. If you haven't got that cover, then maybe you can rig up something with double sided tape or cable ties, i don't think the original cover can be modified too easily for a cis. I guess a few strips of thin foam tape stuck on in the slapping area could reduce the noise.

Best wishes,

Ray

If instead, you were talking about the tubes slapping against the top cover, I usually just leave the cover up if that's a problem.