cencerrear

To clang cowbells, literally — cencerro is a cowbell — and, by extension, to play a musical instrument badly and discordantly, or to sing out of tune: dejó de tocar la guitarra porque solo cencerreaba. A rural-flavored word: the figurative sense is the one a learner is more likely to encounter.

• Se oían las ovejas cencerreando en la ladera. — You could hear the sheep's bells clanging on the hillside.
• El niño cencerreaba en el piano sin haber tomado clases. — The kid banged away tunelessly at the piano without having taken lessons.
• Deja de cencerrear con esa guitarra desafinada. — Stop clanging away on that out-of-tune guitar.

Using cencerrear for any bad noise in general — it specifically evokes the clanking, arrhythmic sound of cowbells or a badly played instrument, not just loudness or unpleasantness generically.