can't carry a tune:唱歌跑调,五音不全,唱的不好:[to be] unable to sing a simple melody; lacking musical ability.
I wish that Tom wouldn't try to sing. He can't carry a tune.
I don't know why Mary's in the choir. She can't carry a tune in a bushel basket.
Joe likes to sing in the shower, though he can't carry a tune in a bucket.
I'd try to hum the song for you, but I can't carry a tune in a paper sack.