It's not just about the noise itself. Gas turbine tends have some higher-frequency noises that's easier to cancel using hydraulic dampers. Diesels have lower-frequency noises, which is harder to deal with.Diesels are not that loud, it is gas turbines that tend to have extreme noise levels at higher output levels. A standard diesel set up is probably pretty comparable to a gas turbine IEPS set up when it comes to noise levels at high speeds.
Overall, a 4000 ton diesel frigate has much less to gain from IEPS than a 7500-14000 ton gas powered destroyer.