The flow field inside a scramjet engine is complex, with unsteady flow features. These unsteady flow features may couple with the scramjet engine’s structure resulting in fluid-structure interactions. Fundamental studies show that such unsteady flows generate acoustic, vorticity and entropy noise and that acoustic noise dominates the other two. To date, the noise level within a scramjet is difficult to predict and has not been measured. Thus, this study focused on measuring the noise levels in a two-dimensional scramjet engine model at a freestream Mach number of 7.3 using the Focused Laser Differential Interferometry (FLDI) technique. For this study, experiments were conducted in the T4 Stalker Tube at The University of Queensland. The FLDI instrument was first built, and the instrument’s response was understood through bench-top experiments. For the bench-top experiments, the instrument’s sensitivity, determined by the beam spacing at the foci was 116 µm, the beam diameter at the focus was 7.7 µm and the f/no was 9.3. The spatial resolution of the FLDI system was determined by traversing a compressed air jet along the beam axis. The 1/e roll-off of the FLDI response along the optical axis was at 10 mm on either side of the beam focal point. A second bench-top experiment to measure the jet from a hot-air gun demonstrated the ability of the FLDI technique to determine the density and temperature of the hot air and corresponding density fluctuation levels. The FLDI system was installed in T4, and freestream density fluctuation levels were measured. The FLDI system was set such that the beam spacing at the foci was 174 µm, the beam diameter at the focus was either 7.05 µm or 5.8 µm and the f/no was 17. By traversing a compressed air jet along the beam axis, the 1/e roll-off of the FLDI response was at 15 mm on either side of the beam focal point. The freestream density fluctuations were measured in the core flow of T4’s Mach 6b, 7, and 8b nozzles. FLDI was also probed inside and outside the core flow of the Mach 6b nozzle. The noise levels in T4 were quantified by normalising the RMS of the density fluctuations by the mean density in Octave bands for frequencies ranging between 22 and 710 kHz. For the Mach 6 flow, the noise levels were higher for frequencies above 400 kHz when measured outside the nozzle core flow. Between 700 and 800 kHz, the normalised freestream density fluctuations were approximately 54 % higher than those measured within the core flow. Between 1.0 and 1.6 MHz the normalised freestream density fluctuations were approximately 60 % higher than those within the core flow. The sound pressure levels (SPLs) increased by 2.5 % in those two frequency ranges. The lower noise levels inside the core flow of the Mach 6b nozzle than those outside of the core flow demonstrate the ability of the current FLDI instrument to reject high-frequency far-field disturbances. The noise levels for the Mach 7 nozzle were similar to those for the Mach 6b nozzle. The RMS of the normalised density fluctuations for these nozzles for the frequency range of 22 kHz to 710 kHz were between 0.1 % and 0.6 %. However, the noise levels for the Mach 8b nozzle were higher and were between 0.2 and 1.7 % for the same frequency range. The SPLs for all three nozzle flows were between 105 and 130 dB. We postulate that the increase in the noise levels for the Mach 8b nozzle flow is due to disturbances originating from a transitional nozzle wall boundary layer. For frequencies above 200 kHz, the noise levels are less than 0.5 % for the Mach 8b nozzle flow and less than 0.25 % for the Mach 6b and 7 nozzle flows. Lower noise levels at these frequencies indicate that T4 is suitable for conducting fundamental studies in the hypersonic flow regime and scramjet testing. The FLDI instrument was then used to measure the noise level generated at five locations within a scramjet engine flow path. Hydrogen fuel was injected from a single porthole injector that was inclined at 45◦ to the local surface direction and was located on the intake of the scramjet. Measurements were made for equivalence ratios of 0.15 and 0.23, and tests were conducted with and without tripping the boundary layer. Measurements were made for unfuelled, combustion-suppressed and combustion-on conditions. Noise levels were deduced for frequencies between 22 kHz to 710 kHz. Two of the five probing locations were in the intake flow path and downstream of the fuel injector. The other three locations were towards the front, middle and end of the combustor. Thus, this system allowed quantification of the noise generated by different features in the scramjet engine flow path. At the first measurement location, which was 15 mm downstream of the fuel injector and 4 mm above the intake surface, the normalised density fluctuations measured for the unfuelled and untripped cases for frequencies between 100 kHz to 710 kHz were approximately double those measured in the freestream. This provides evidence of a significant amount of noise generated by the boundary layers formed on the intake of the scramjet engine. Fuel injection and tripping the boundary layer increase the noise levels, but the effects due to these diminish with increased distance along the flow path. Inside the scramjet combustor and among the three conditions, a trend of increase in the noise level due to combustion is observed across the three probing locations within the combustor. However, the overall increment in the noise level is modest between the three conditions and across the three probing locations. For all three conditions and across the three probing locations, the normalised density fluctuation levels range between 0.3 and 1.9 % and the SPLs between 150 and 170 dB. There were only subtle changes in the noise levels between the two equivalence ratios. Therefore, this study concludes that, at least for the current scramjet configuration and fuelling levels, fuel injection, shear layer instabilities, and supersonic combustion processes do not introduce significantly higher noise levels in the scramjet flow path —implying that the base hypersonic flow field inside the scramjet engine is the main contributor to the noise field. Further investigation is needed to check the applicability of these results to scramjet engines with flow paths having more complex flow fields, fuelling schemes and higher fuelling rates. The low-frequency acoustic loads and fatigue limit, which may result in structural failure, have frequencies lower than those measured in this study. However, this study is a first step in characterizing the acoustic loads generated within scramjet engines and helps understand the mechanisms leading to noise generation and what noise levels would be generated inside a scramjet engine. Further, this study provides a path to explore low-frequency noise and ultimately help engineers to design hypersonic vehicles with a lighter structure (by driving down uncertainties), leading to an increase in payload and efficiency but without compromising structural integrity