FWIW just a few notes on piston noise, since the subject has been mentioned.
I spent several years doing piston development on various engines.
First thing to understand is that they are not round, not straight, the gudgeon (wrist) pin is not in the middle, the ring lands are all sorts of different shapes and not necessarily even concentric with each other.
As the engine runs, the piston will tilt, sit against one side of the bore, tilt again, reverse sides, etc, typically doing 6 or 7 tilt reversals during a cycle. This is due to inertia effects, gas pressure, and friction.
Each time it tilts it can result in noise. The most noise, and the most noticeable and annoying noise, is typically if the top land (above the top ring) hits the cylinder bore. The crown is the stiffest and heaviest part of the piston and will make a knocking/tapping sound which is quite distinctive. Top land clearances are kept at a minimum, allowing for thermal expansion (piston crowns can run at up to 300C) because this is the area where most HC emissions originate due to trapped fuel which won't burn in small gaps. However there is the risk of hard contact and noise with small clearances. The top land is usually tapered and sometimes offset to one side to reduce the tendency for contact with the bore.
Land and ring groove details are complex, to allow management of oil and gas flows. Gas pressure gets behind and between rings and can influence dynamic movement of the rings, occasionally lifting rings off the bore surface or causing "flutter" where it rattles up and down in the groove. Ring geometry and flexibility is another huge subject.
Skirts profiles are developed to support the piston best once it is at full operating temperature. They are generally hotter at the top and cooler at the bottom, so the skirt is usually a pear-shaped barrel profile. The piston expands differently in the thrust axis and the gudgeon pin axis due to the masses of the pin bosses and thus the temperatures are different. This means the skirt, and sometimes one or more ring lands, are oval (major axis on the thrust line, minor axis on the pin axis). However it isn't usually a simple oval, it is a shape which allows for the differential expansion of the piston and the bore (bores seldom stay round when hot) so can have "corners" at the edges of the thrust panel. Some skirts have slightly raised pads to act a bearing areas to reduce friction, plus low friction coatings, but the profile still needs to be made to suit the expansion. Skirts are generally reasonably flexible so "soften" the impacts reasonably effectively. While cold or part warm the support might not be ideal and you often get different noise characteristics during cold start and warm-up, and it is very load dependent. You can get light-load rattle where the gas pressures are low and inertia forces are dominant, put on slightly more load and the rattle goes away because the tilt points change.
Gudgeon pins are offset towards the thrust side by typically 1.0-1.5mm to encourage the piston to tilt to the thrust side due to inertia forces as it approaches TDC especially at low speed/idle to reduce noise. Too much or too little offset can make things worse. One engine family I worked on has 2 variants with different capacity/strokes, with different con-rods, and those pistons ended up with different pin offsets to minimise cold start rattle.
In my experience Honda car engines typically are not the quietest pistons, but they are pretty bomb-proof.
Electric motors are much simpler. Perhaps it's the future?
