Sounds like it may be time to take your car in for some maintenance. 😀
It depends on what you mean by "simple". Here is my version of "simple" -- any given mass attached to the end of a spring of a given stiffness has a natural frequency of vibration. If you change either the mass or the spring then that frequency also changes. If you want more, then ....
Suppose that we "excite" this spring-mass system by poking on it with something (a bowl gouge, for instance), the spring-mass system will respond by vibrating back and forth (or perhaps, to and fro) at its natural frequency until the vibrations eventually die down. (The vibrations die down because there is a third component to this system that we initially overlooked called a damper that is absorbing the energy of the vibration).
Now, suppose that we decide to poke this spring-mass-damper with our blunt instrument at exactly the same rate as the system's natural frequency of vibration. We will see that the amplitude of the vibrations grows ever larger until something breaks (mass comes loose from spring, smacks our investigator holding the blunt instrument and then rolls around on the floor.
Seeing that our previous action was a bad idea, we decide to find out what happens if we poke the spring-mass-damper system with the same blunt instrument at a rate that is slightly slower or faster than the system's natural frequency of vibration (a.k.a., "resonant" frequency). We discover after much wear and tear on our investigator that as our chosen exciting frequency approaches the resonant frequency of the system, the amplitude of the oscillations (i.e., the to and fro vibrations of the mass on the end of the spring) grow in magnitude. We also discover that when we excite the system at a frequency sufficiently removed from the system's natural frequency that the exciting frequency no longer has much of an effect on the amplitude of vibration of the system.
In the real world we find that masses, springs, and dampers rarely look like the classic examples seen in freshman physics textbooks. We can often identify a mass, but the spring and damper may not be as obvious. To make the picture even muddier, these systems rarely live in isolation. Most everything around us (a woodturning lathe, for example) consists of a large collection of masses, springs, and dampers that all interact with each other to some degree. An out-of-balance hunk of wood spinning on a lathe is both a source of excitation and a mass coupled to another mass which consists of the lathe body through a rather stiff spring consisting of the drive train. At the same time, the drive train itself is a spring mass-damper-system consisting of the spindle, bearings, belt, and motor. And the motor itself when being powered under load is working to maintain a certain slip frequency by changing the current through the field windings to provide the needed torque. When the load (i.e., the out of balance spinning hunk of wood being intermittently cut with with a blunt bowl gouge) is not reasonably constant then the drive train reaction also becomes part of the overall system stability. The most obvious dampers in this overall system might be your bags of sand, cement, or deer corn on the bottom shelf of the lathe, but the complex geometry of the lathe body itself usually provides most of the damping.
-e-, where have you been? Good to see that you are still alive.
