Why Do Certain Sounds Bring Sadness To Mind?

Why do certain sounds bring
Sadness to mind?
I find
That when birds sing
And engine’s notes are in distance
Lost, that my resistance
To melancholy
Is low
And I go
In search of Keat’s Nightingale.
Yet tis folly
I think
To drink
Too much of Keat’s brimming cup.
But o how sweet it is to sup
At melancholy’s table
Provided we are able
To partake of her store
For a while,
Then, with a wisthful smile
Withdraw.