There’s a word for a sudden, startling realization, but it’s not coming to me.
Yesterday I was investigating the source of a periodic “whooshing” noise I could hear while on my bike. I can’t hear very well at the moment, as ear infections recently damaged my ear drums and whatever else is in there, so I knew this noise must be loud and not to be ignored. After studying the Clymer KLR 650 manual for a while, I had assembled a short list of possible causes, then went to work. The first step was to reproduce the noise: check, there it is, upon starting, warming and throttling the machine. The periodic frequency didn’t change directly with RPM, though it did vary for other unknown reasons. The first fix on my list was to reset the balancer chain tensioner (doohickey). After, I again checked for the telltale “whooshing” — still there! I didn’t want to take the next step: inspecting the valve shim clearances with the cams, as this meant major mechanical work and would take some time and possibly parts (new shims).
Contemplating this while listening to the “whooshing” a bit more, I flicked off the ignition without much thought, killing the engine. There must be a simpler explanation! The bike only has 8200 km on it. Did it overheat without my noticing? Dang! Then I realized I could still hear the “whooshing” noise. The KLR was off. It took a full minute of denial before accepting the truth: the sound I had been hearing was my own heart beat, isolated by my brain and the natural roar of the bike, and amplified by my messed up ear drums. We automatically filter out the din of the motor and other periodic sounds our brains deem useless, and we isolate and amplify those judged to be important. Apparently blood rushing by my temples is something to which I should pay attention.
I’ll get a friend to listen, but I’m pretty sure this case is closed.