True. But a well built and maintained bike, unlike a race motorcyle or high performance automobile doesn't put down enought power to flex the chassis and expand the joints to allow/introduce a vibration from steerer tube/headset, ball joint or suspension bushing. A vibration by defintion is a harmonic due to flex and most likely on the bike due to momentum and weigh would start with wheels and/or fork.
You can induce the harmonics without a lot of effort. It's a very low frequency vibration. Essentially, the bike is making tiny back-and-forth turns around the headset axis. No "chassis flexing" or "joint expansion" is necessary.