They check engine noise by a drive by sound test, this is not upto the pits people to perform, and thus never been performed in WA.
The pits give their opinion on whether they think it is too loud and it is upto you to prove them wrong via an engineers report.

check ADR 28/01

"2. Procedure for Vehicles in Motion
(Refer to diagram - Section 4)
2.1 Site for tests on vehicles in motion.
2.1.1 The measurements shall be made at an open site where the ambient and wind noise levels are at least 10 dB(A) below the noise level being measured. The site may take the form of an open space of 25 m radius having a central part of at least 10 m radius, practically level, consisting of concrete, asphalt or similar material and not covered with powdery snow, tall grass, loose soil, ashes or the like. During the test no one shall be in the measurement area except the observer and the driver. Their presence must have no influence on the meter reading.
2.1.2 The surface of the test track used to measure the noise of vehicles in motion shall be such as not to cause excessive tyre noise.
2.1.3 Measurements shall not be made under adverse weather conditions. Any sound peak which appears to be unrelated to the characteristics of the general sound level of the vehicle shall be ignored in taking the readings. If a wind guard is used, its influence on the sensitivity and the directional characteristics of the microphone shall be taken into account.
"