Most likely the toll of a bell, the action would be tolling the bell. You could also use knell for the sound.
Slow ring
Knell is the sounding of a bell, particularly a church bell for a funeral.
A knell is the sound of a bell, especially at a funeral.
The definition for knell is the sound made by a bell. It typically describes the sound of a bell that is rung for a funeral or death.
Wind-chimes.
A knell is typically produced by ringing a bell or the sound of a bell tolling. It is often associated with a funeral or death announcement.
The part of the bell that makes the sound is called the clapper. This is the hanging piece inside the bell that strikes its sides to create the ringing sound.
bong, call, chime, clang, knell, peal, signal, sound,
One example of a warning sound starting with "kn" is a knell, which is the sound of a bell ringing solemnly, often to mark a death or funeral.
Ring, ding, ding-ding, etc.
Most likely the toll of a bell, the action would be tolling the bell. You could also use knell for the sound.
a bell