In a loud, loud manner that produces a lot of sound or makes a strong acoustic disturbance.
From 'noise' (Old French 'noise' meaning 'quarrel or commotion') plus the adverbial suffix '-ly.' The word 'noise' has always carried connotations of unwanted sound, and 'noisily' preserves that judgmental quality.
Interestingly, what counts as 'noisy' is cultural—some people find babies crying noisily normal, while others find a sniffling nose in a quiet library unbearably noisy. The Romans didn't even have a word that quite meant 'noise'—they'd say 'strepitus' (clattering) or 'fragor' (crash)!
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