Two problems related to engine clicking and tapping noises have been reported for the 2008 Toyota Sienna. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2008 Toyota Sienna based on all problems reported for the 2008 Sienna.
Upon exiting freeway in butte, mt, and slowing done for red light at bottom of ramp, heard tapping noise coming from engine. Drove one block to gas station, and while pumping gas, noticed large quantity of engine oil puddling under the engine. Had vehicle towed to Toyota dealer, who determined that oil cooler hose had ruptured. Fortunately, no apparent engine damage. After some research on Sienna owners' forum, learned that this was a recurring problem on certain Toyota models in certain years, including the 2008 Sienna with tow package like ours, and that Toyota had put out a TSB on this, but apparently had never informed owners. It took 4 days for the replacement hose to arrive, and the repair cost $520. This incident occurred while my family was far from home (silver spring, MD) on a cross-country trip and thus forced them to cancel part of vacation and spend extra $$ on hotels and a rental car. But it could have been much worse - the oil could have drained while at speed on the highway, ruining the engine, stranding my family in an isolated area or causing an accident or engine fire and possible injuries. Given that Toyota was aware of the problem, it could have informed us so we could have had the hose replaced before it failed.
Early am on 6/1/10 I was driving to my cabin in the country and heard a soft popping sound, stopped my car and smoke began flowing out all opening around the hood, when I looked under the car I saw fire falling to the road. I went to the passenger side and opened the door only to find that area filled with toxic fumes, shutting the door I realized all was hopeless except to get away from the vehicle. Within seconds my car was engulfed in flames. I ran as fast as I could to get help. Had I been less alert, inactive, less proactive I would have probably died. The car was purchased new in Nov, 2008 and had a little over 10,000 miles. There was no smell of fuel or another strange odor. The car was burned totally, with nothing remaining except the steel frame.