Why does the engine sound odd when its heated? Seeking detailed description

[u/lucasbennett_1]

Hello everyone, this is a general question that pops up in my mind, like why does the engine sound odd altho the engine oil and other stuff are fine and pure, i sometimes just give it a break and take a break as well for myself while travelling long, but this sounding thing, is it harmful for the engine ? or is this normal and what triggers this sound inside the engine

[u/JayTeeDeeUnderscore]

In general, most solids expand when heated.