>>> I think the idle on the QS was a little louder, but not a lot. <<<
Well if idle is louder, it will tend to be louder when loaded and revved too.
This makes two people saying that the QS seems to be a bit louder than a Lotus Stage 2, which is different than the QS claims.
Sounds like it's meter time, and ideally with a spectrum analyzer.
Use the A-scale on an SPL meter, slow response if you try this out...that's what tracks and the SCCA use for such matters. There is more to it than that of course.
To get relative dB you can just keep distances constant and go for it to get a sense of things. If you want to get SPL numbers that others can duplicate and that are more credible you need to start doing things like testing with the cars far away from anything, more accurate distances, heights and angles. For example inside of a garage would throw things off. If you are careful, deliberate sort, you can duplicate official tests though with about a dB or so.
Stan