Variations of this idiom with the same meaning:
can’t carry a tune in a bucket;
can’t carry a tune in a bushel basket;
can’t carry a tune in a paper sack.
Examples from the web:
- Mark: “Sing with us!”
John: “Sorry. You wouldn’t want me to. I can’t carry a tune.”
- I invited Sarah to join the choir but she refused, she told me she can’t carry a tune in a bucket.
A short article I found while surfing the web: “Can’t Carry a Tune? Work Out Your Vocal Muscles”. by Lena Groeger
This is the link (I opened it with Lingro, in this way if you click on a term that you don’t know, you can read the definition in English): http://lingro.com/translate/http://www.scientificamerican.com/article/physically-out-of-tune/
In short, the article is about physical reasons of bad singing.