Modern customer and legislation requirements have led to a high demand for energy efficient low pollutant engines. Such efficiency is commonly achieved through the deployment of turbochargers, in both Diesel and Otto engines. This strategy, replacing high displacement engines, is a tendency commonly designated as downsizing. This allows higher power outputs, increased energy efficiency and lower emissions allied with lower weight on the vehicle’s power pack. Those turbocharger units consists basically of a compressor connected by a solid shaft to a turbine, which is propelled by the exhaust gases in order to compress (boost) the intake charge air to the engine, increasing pressure in the system.The turbocharger system is commonly a source for synchronous/sub-synchronous noises, as well as compressor or turbine related NVH issues, which must be mitigated in order to fulfill customers’ expectations. Subjectively, a high frequency whistle noise was audible in the cabin for an entry-level vehicle cabin during parking maneuver - throttle “blips” in a low displacement 4-cylinder diesel engine during design validation phase. Objective noise measurement confirmed the issue was not unbalance related.A detailed investigation was carried out to identify the source of the high frequency whistle. The present work shows the study performed to determine if the noise was related to component design itself, prototype manufacturing or instrumentation interaction with the system. The first section briefly describes the turbocharger system and aspects. The second part describes the root-cause investigation and analysis, with suggested corrective action. The third section shows the corrective action evaluation and derived lessons learned from the process.