This problem has existed since we bought this luxury trash van on wheels. I have had nothing but problems with this vehicle since we bought it. The serpentine belt started to squeal ungodly on cool damp mornings around 20k miles until it got so loud we had to have it replaced. I asked the dealer to examine the pulleys and they reported all to be fine and billed me for two belts and installation. Since then we have had three complete sets of belts in 90,000 miles and this set shredded and damaged the lower timing belt cover. I will post pics when I perform the repair myself. My first and last Toyota!

Purchased vehicle brand new. With only 45,000 miles, the engine belts flew off. Had it towed to Toyota dealer. At first, I thought that it was only a bad belt. The dealer said the real issue was a bad harmonic balancer pulley (the big pulley on the end of the engine crankshaft). The part appeared as if it had rubbed or scraped on something. Anyway, the repair cost $500.00 and Toyota did not cover it under warranty. Our older Sienna never had such a problem and still runs fine with 200,000 miles. I owned a 1988 Toyota Supra that I drove to 249,000 miles with no major issues.