talking about engine noise

hai you owners of kx, cr, yz, rm and probably also huskies and ktms.
occasionally we hear owners complaining about their engine noises.
What i want to know is can we pinpoint that specific noise and can we blaim a specific part of the engine regarding that noise.
Do some manufactures, like kx, built engines with more freeplay?
So are their owners who experienced this noise, and for example switched from one brand to another and thus have a good experience regarding above question. So feel free to shine some light on this issue. Maybe we can ease some minds regarding engine noises.