Now I have another question - why is that the analogue tuners suffer more from this than the digital ones ?
There is very complicated answer for this. Let me explain it in a simple way. Consider you have letter written on paper and want to send long distance. You will put it in some envelop with identification tag and sent. Receiver receives, removes envelop and read that letter.
Human/music sound is one frequency and you need to transmit in air for long distance. You put it on a carrier that is 88-108MHz for FM or 530-1700KHz for AM. You have to receive that carrier, remove that carrier and retrieve sound.
That retrieval is done by analog or digital processing.
Analog processing used variable caps and variable (tuned/preset) coils. Mixes some local generated frequencies which converts some intermediate form. That intermediate form contains that sound and further module does retrieval of that sound. All user interaction with knob is converted to mechanical movement and change in tuning devices within preset ranges. If physical mechanical (preset) state of these tuned devices changes then you get misalignment in any of the detection modules. Dust, rusting and displaced cores etc could do that misalignment.
Digital tuner works with the help of some microprocessor. It receives carrier, converts to intermediate format using tuned voltages controller by microprocessor. All user interaction is detected by microprocessor which changes various voltages and band, stations gets tuned. Now here sound detections is done by frequency division etc. There are no mechanically tuned devices. Still there are some filters and oscillators which are fixed callibrated. There are some reference voltages fixed and aligned. These may go out of alignment. Still these are very less in number as most of the parts are electronics devices and no changing of mechanical or physical state of tuning devices.
Forgive me, I avoided using words like superheterodyne, down conversion, modulation, demodulation and crystal clocks etc. That was done wilfully to avoid technical jargon.