I see what you're saying - but I was at full throttle the whole time. At full throttle, what I explained above was happening. Try it yourself. Start out at full throttle with all energy levels at 50%. Now increase either weapons or shield settings and you'll hear the engine volume level increase. Now, if you reset all of the levels to 50% and increase the engine energy level to full while at full throttle, you'll hear the engine volume decrease. That doesn't seem right.
It seems that if you funnel all of your energy toward your engines, the volume level of the engines should increase, yes? But that's not the case - when increasing the weapons or shield energy settings to maximum, that's when the volume level of the engine sound increases. If you put max energy toward engines, it gets quieter. That doesn't make sense.