the tune the old cow died of

разг.; шутл.

режущий слух мотив, какофония; скучная, плохо исполняемая музыка; ≈ от этого мухи дохнут [выражение ведёт происхождение от старинной баллады:

There was an old man, and he had an old cow.

But he had no fodder to give her,

So he took up his fiddle and played her the tune:

‘Consider, good cow, consider,

This isn't the time for the grass to grow.

Consider, good cow, consider’]

It was kind of poor, and when he was going to start on the next verse one of them said it was the tune the old cow died on, and another one said, ‘Oh, give us a rest’... (M. Twain, ‘Life on the Mississippi’, ch. III) — Выходило у него неважно, и, когда он начал следующий куплет, один из сидевших высказал догадку, что именно от этой песни околела старая корова, другой же сказал: "Дай нам передохнуть".

...that is enough of the tune the old cow died of; take and play something to keep our hearts up. (Ch. Reade, ‘Love Me Little, Love Me long’, ch. III) — ...сыграйте что-нибудь повеселее, хватит с нас этой унылой музыки.