Wastegate chatter myth
There is a common myth in the automotive world about so called "wastegate chatter", a noise created on lifting off the throttle in a turbocharged car. The sound is commonly described as a chipmunk or a rattlesnake and is often stated incorrectly as being a result of the turbo's wastegate closing.

The noise is in fact the air compressed by the turbo passing back through the compressor housing of the turbo after having hit the now closed throttle plate. This is also known as Compressor Surge and over time can result in significant damage to the turbocharger. It damages the turbocharger by bringing the compressor blades (which spin in excess of 100,000 RPM) to a near dead stop almost instantaneously. This puts an enormous amount of stress on the blades which causes them to fatigue faster. To avoid this turbocharged cars will use a blowoff valve (BOV), which allows the extra pressurized air in the intake out. However, in some cases, i.e. where it doesn't open fast enough or is setup to only react to high boost, some chatter will remain.

The chatter noise is very noticeable on WRC Rally cars, where no BOV is allowed.

"This has also been known as "Turbo Flutter" and in some cases, adding a BOV can increase the flutter especially if you have an intake system. Once the air hits the closed plate, the only path it has to exit is through the intake."