I can't seem to find Spirit #17 in the "Spirits of Aranna" quest in Act2.
It says the ghost can be found under the city of Kalrathia. I found a elevator to a basement under the tavern but it's a dead end with nothing but some rebels (who aren't there anymore once I kicked the Mordin out).
Just keep playing. The main quest line will eventually take you under the city.
SWC
Sir Edmund:"Should you obey the lord who asks you to put a village of innocents to the torch? Is that chivalrous? Is it noble?" Me:"It's a great way to get promoted, I know that much."