Drops

Amaziah then said to Amos, “Leave, you visionary! Run away to the land of Judah! Earn your living and prophesy there! Don’t prophesy at Bethel any longer, for a royal temple and palace are here!”
Amos replied to Amaziah, “I was not a prophet by profession. No, I was a herdsman who also took care of sycamore fig trees. Then the Lord took me from tending flocks and gave me this commission, ‘Go! Prophesy to my people Israel!’ So now listen to the Lord’s message! You say, ‘Don’t prophesy against Israel! Don’t preach against the family of Isaac!’ Amos 7:12-16

A Raindrop's Life, Neelesh Jain, Graphite on Paper

Constable's comments on the Hebrew word for preach: 

"Amaziah had told Amos to stop prophesying, namely, to stop preaching (v. 16). “Preaching” is from a verbal root meaning “drip” (Heb.natap), as the heavens drip rain (Judges 5:4; cf. Amos 9:13). The idea is that Amos should stop raining down messages from heaven on his hearers. True prophets were people who spoke fervently for Yahweh."  -Constable's Notes

From Strong's:

נטף
nâṭaph
naw-taf'

A primitive root; to ooze, that is, distil gradually; by implication to fall in drops; figuratively to speak by inspiration: - drop (-ping), prophesy (-et).


In the passages referenced, there is this continued idea of raining down or flowing:

O Lord, when you departed from Seir, when you marched from Edom’s plains, the earth shook, the heavens poured down, the clouds poured down rain. Judges 5:4

“Be sure of this, the time is coming,” says the Lord, “when the plowman will catch up to the reaper and the one who stomps the grapes will overtake the planter. Juice will run down the slopes, it will flow down all the hillsides.Amos 9:13