Notes to Macbeth, Act 3, Scene 5, line 33:

"Come away, come away, etc."

Act 4, Scene 1, line 39.
It is generally thought that the song referred to by its first line, "Come away, come away," is the same song used later in The Witch (c. 1615), a play by Thomas Middleton (1580-1627). The play is online: See The Witch, by Thomas Middleton.

Below are the lyrics. As you can see, in The Witch, there's not only a song, but a rather elaborate production number, involving the descent of a spirit in the shape of a cat, and the ascent of Hecate with the cat-spirit and five other attendants.

Come away, come away,
Hecate, Hecate, come away.

I come, I come, I come, I come,
With all the speed I may,
With all the speed I may,
Where's Stadlin?


Where's Puckle?


And Hoppo, too, and Hellwain, too;
We lack but you, we lack but you.
Come away, make up the count.

I will but 'noint, and then I mount: I will just anoint, and then I will ascend. Apparently some sort of mock-religious ceremony is indicated here.
I will but 'noint, and then I mount.

A spirit like a cat descends.

There's one comes down to fetch his dues,

coll: a neck hug.
A kiss, a coll, a sip of blood,
And why thou stay'st so long
I muse, I muse,
Since the air's so sweet and good.

Oh, art thou come?
What news, what news?

All goes still to our delight,
Either come or else
Refuse, refuse.

Now I am furnish'd for the flight.

Hark, hark, the cat sings a brave treble in her own language!

HECATE, going up :
Now I go, now I fly,
Malkin my sweet spirit and I.
Oh, what a dainty pleasure 'tis
To ride in the air
When the moon shines fair
toy: play, caress.
And sing, and dance, and toy, and kiss;
Over woods, high rocks, and mountains,
Over seas, [over misty] fountains,
Over [steeples,] towers, and turrets,
We fly by night, 'mongst troops of spirits.
No ring of bells to our ears sounds,
No howls of wolves, no yelps of hounds,
No, not the noise of water's breach
Or cannon's throat our height can reach.
No ring of bells, etc.

[Hecate and her spirit ascend out of view.]