What is an example of an onomatopoeia that starts with the letter X?

An example of an onomatopoeia that starts with the letter "X" is "x-ray," often used to describe the sound of an x-ray machine or the imagery associated with it. While "x-ray" may not be a traditional onomatopoeia like "buzz" or "bang," it evokes the imagery of the sound associated with the medical procedure. Unfortunately, Words that are true onomatopoeias starting with "X" are quite rare.