The 40 section of my 60/40 second row seat shakes very noticeably in my 2003 sequoia with 63k miles. It has done this since I bought it with 54k miles. The dealer says they cannot find anything wrong with it. Balancing the tires helps for a few weeks but the shake always comes back. I have replaced shocks on all corners and recently put on a new set of tires. The shake is still there. It is VERY annoying. Other than this problem, I absolutely love my Sequoia. Anybody else experience this? Any ideas?