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#11
Not all motherboards have a speaker attached as some cases don't have them and or the motherboard manufacturer doesn't supply one. No speaker no beeps.
Speakers for POST sounds come with the case. They used to have them mounted to case with a 2 pin connector tail for mobo plug in. My HAF 932 case had a tiny loose speaker that plugs to mobo. Bet most mobos have pins ready, bet you can buy a speaker for it if not with case.
POST beeps will answer questions when OS will not boot.
POST is for the mobo, ram and vid card and keyboard, mouse if you want. You do not have to have a drive connected for a good POST.