An idiomatic phrase meaning that you are aware of a coming change based on minor signals you've observed over time

The (hand)writing is on the wall

dictionary.com

a premonition, portent, or clear indication, especially of failure or disaster: The company had ignored the handwriting on the wall and was plunged into bankruptcy.

phrases.org.uk

Imminent danger has become apparent.

TFD

the likelihood that something bad will happen

based on a story in the Bible about Daniel, who reads the handwriting on the wall that predicts the end of the kingdom of Babylon

You often hear people say "There is something in the air".
Sometimes, there has been something in the air.

It is an allusion to a dog sniffing the air, detecting the smell of something far away.

Assuming OP specifically wants an expression relating to hearing ground tremors, the most relevant idiomatic expression I can think of is...

picked up rumblings

That's an estimated 126 written instances, the vast majority of which are OP's figurative sense.

You can say you are keeping your ear to the ground meaning you are alert for signs of change, but I think it would be somewhat strained to say "I am aware because I'd been keeping my ear to the ground." Better would be "I'd picked up on that".

Fig. to devote attention to watching or listening for clues as to what is going to happen. John had his ear to the ground, hoping to find out about new ideas in computers. His boss told him to keep his ear to the ground so that he'd be the first to know of a new idea.

keep an ear to the ground. (n.d.) McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. (2002). Retrieved June 10 2016 from http://idioms.thefreedictionary.com/keep+an+ear+to+the+ground

pick up on Informal
1. To take into the mind and understand, typically with speed: is quick to pick up on new computer skills.
2. To notice: picked up on my roommate's bad mood and left him alone.

pick up on. (n.d.) McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. (2002). Retrieved June 10 2016 from http://idioms.thefreedictionary.com/pick+up+on