O explicatie ceva mai tehnica:
The noise is in fact the air compressed by the turbo passing back through the compressor wheel of the turbo after the airflow is abruptly halted by the throttle plate closing, called compressor surge. However, in some cases, i.e. where the throttle plate doesn't open fast enough or is set up to only react to high boost, some chatter will remain. Surge can occur on diesels when the turbo is attempting to pressurize the air at a higher pressure ratio than the compressor wheel can flow at a given speed. Most Diesel engines have no use for a blow off valve as they do not have a throttle plate.
The chatter noise is very noticeable on World Rally Cars, where anti-lag is used.
It is commonly heard more clearly and may be more prominent on cars with modified intake silencers, up-pipes, downpipes, or an oversized wastegate incorrectly matched to that specific engine. Also, vehicles using on/off solenoids to control boost can do this under certain conditions. It is not harmful to the engine.