Convert to EFi.

ERST's chatter, infact every turbo chatters to an extent as the throttle closes and the air is forced backwards through the compressor blades. It is the sound of the blades 'chopping' the air that can be heard. The chatter from the ERST turbo is muffled by the fact that there is a metering head and an air filter for the sound to pass through, so it can only vaguely be heard.

Make sense?

So, by getting rid of the metering head, you will hear the chatter!