What is the fine-grained topic of the following text: I thought a lot of the rasp also had to do with the dual piped exhaust design and the firing order of the motor (and thus exhaust pulses in each separate pipe -- which is why it's only heard at certain RPM (aka at certain pulse "frequencies" as the gases bounce off the walls of the 2 pipes)? Only return the topic.
Exhaust sound characteristics and influences