Paul, its probably induction noise rather than exhaust noise.
My ST sounds much louder than the 998 when riding it, but to those not on the bike it is the other way around. Something to do with the long induction tubes on the 998 compared to no top on the air filter for the ST
I did buy some inserts but thought they looked pants, so have not fitted them. I too wear ear plugs all the time.
[Edited on 21-2-2005 by John W]