The damping material can help by reducing case vibration, but it's not likely to cure a jetliner sound issue.

Your best bet is to investigate where the noise is coming from. It is most likely to be either the CPU fan or the power supply fan. If it's the CPU fan, then consider upgrading your heatsink to a larger copper heatsink that will take an 80mm fan, combined with a Papst/Panaflow fan.
If it is the PSU fan, then putting a temp-dependant fan in might help. Either that or a manually adjustable fan.

You might also want to consider adding a quiet case fan blowing into the case. This will help you to lower fan speeds elsewhere without giving up too much in terms of case temps. It will also have the added benefit of balancing out case vs ambient air pressures, so less dust will be sucked into the case. (Remember to put a filter over the case fan!)