I'm not sure what the "rent related phrases" are but just looking at the trend chart for "rent" reveals a similar pattern [1]. "Numbers represent search interest relative to the highest point on the chart."

[1] http://www.google.com/trends/explore#q=rent&geo=US&cmpt=q

My problem with it is a bit more basic: why bother showing stats on Google searches as an "indicator"? Why not just go straight to the stats on rental demand vs. supply?

I tend to view the absence of a y-scale to be very telling ;-)