Well without further analysis or information, a short answer would be that your engine is BROKEN.
By replacing the chain and tensioners.
rattling or clanging
I would first check the timing belt/chain and alternator pulley for any odd damage. Its possible the timing is off, or the belt/chain was put on incorrectly.
When you here a rattling noise from the engine at idle.
i had a rattling noise in my 2000 ls, was told it was worn tensioners on timing chain. i guess they are made out of a poly carbon and wear after a while. haven't fixed problem yet...
Toyota claims that it should last the life of the vehicle. Unless you have a strong reason to believe that the chain has to be changed (rattling, clunking noise and etc). Otherwise you do not have worry about that.
Normally you will be able to hear the timing chain rattling inside the cover. You may also experience problems keeping the engine in time. A timing chain will last the life of the engine under normal circumstances.
according to the service manual the cam chain is not adjustable. you must replace it or the tensioner if it is noisy. mine make's a rattling noise at idle and need's to be replaced.
lifters are beginning to go. timing chain (if vehicle is equiped) may be coming loose. and or exhaust pieces are loose.
The timing "chain"will start rattling at around the 100k to 110k mark. This is when it should be replaced
Car will run rough ,backfire and you may be able to here it rattling.
With a timing belt, it should be changed around 90,000 miles. A chain can last much longer. Have your mechanic check it to see if there is any rattling or loosening on the chain. Some timing chains can last the lifetime of the car.