If you can get enough volume out of your intercom system to make it feasible, wear a set of those squashy earplugs (EAR, Bilsom etc.) as well as your headset / helmet.
It reduces the available volume level, of course, but I find also makes it easier to pick out what's being said on the radio because the ambient noise is filtered out that much more.
The bonus is that you are being doubly protected from the insidious effects of harmful aircraft noise. The down side is that if you share your ICS with others and they aren't similarly protected, you may have to have the radios etc turned up to annoying levels for them.
I've had ringing in my ears for years from turbine noise, and I'm trying my best to avoid ending up with two hearing aids like my Mum has!