Well I have now have brand new leaf springs from Nissan. They seem a little stiffer then the old one's, I hope so! Haven't hand time to really test them, but I will know tomorrow.
I have a 2007 Xterra manual transmission and my vehicle does the same thing with people in the back seat.
It makes a thud / thunk noise over some dips or over some speed bumps.
The dealer says it's "the design" and they recreated the issue with both a new 2008 and my 2007. Seems like a poor design to me considering the Xterra is supposed to be rated to hold over 1000lbs including cargo.
This is a safety issue to me. The first time I heard the noise I thought I hit something in the road.
Well the sound that your hearing is the rear end bottoming out. I finaly got Nissan to replace my rear leaf springs and that has seemed to help. The only way I got anything done was going through Nissan directly. Getting started through your delar ship is a waste of time. Call Nissan!! It is a safty issue!