Chatter is caused by air returning through the turbine blades when the throttle is closed. This air is going backwards so will stall/slow down the turbo as it passes through creating a chattering noise. The MFI system dampens this noise as the air flow sensor plate in the metering unit closes because the throttle is closed and the ammount air the engine requires is reduced.

A EFI system has no sensor plate so the chattering can be heard directly through the air filter.

I am running MFI and i get some ammount of chatter, if you are using a dump valve this will reduce the ammount of chatter as its designed to bleed off the excess air so it doesnt return through the turbo.