Five years ago I had amassed enough miles on Southwest for a free flight to Florida. I also had a fortuitous break in my work schedule that allowed me the freedom to use that free flight to travel to Florida to watch the second-to-last launch of the Space Shuttle. This is something I had wanted to do since I was a nerdy little kid, and so as a nerdy middle-aged adult I was thrilled to finally be able to make that wish come true.
After taking the last flight to Orlando I checked into a cheap hotel on the east side of town where I slept for a few hours until my alarm awoke me at 3am. I then drove for about 45 minutes until I reached Titusville where I claimed a spot on the Max Brewer Bridge that I had heard was a good place for non-VIPs such as myself to view launches.
I then waited for about four hours until the launch itself.
I had always been told that that launches are incredibly loud. Located as I was almost twelve miles away from the action, the event for me was utterly silent. The only indication that the launch sequence had started was when the clouds of steam began to boil out to either side of the launch pad. The Shuttle's three main engines actually ignite about four seconds prior to its actual liftoff. This allows them to come up to full power and to identify any issues prior to the launch (a handful of launches were aborted when the engines automatically shut down during these four seconds). This time also allows the shuttle stack to self-resolve its twang.
To explain what I mean by "twang" I first need to describe the general design of the shuttle. Two white Solid Rocket Boosters are strapped to either side of a single large and orange External Tank. The winged Shuttle Orbiter with it's three main engines are then attached to one side of this External Tank. This configuration creates an asymmetrical assembly which is somewhat unusual in spacecraft design.
An artifact of this design - and the fact that the Main Engines start a few seconds before launch - is that the entire assembly flexes several feet in response to the asymmetrically applied thrust of the Shuttle Orbiter's main engines. It then "bounces back" to its original condition an instant before the Solid Rocket Boosters are themselves ignited and liftoff occurs.
This phenomenon can be seen most clearly at the extreme end of the assembly at the top of the External Tank: