My tercel (96 / 166K miles / 4 cylinder) appears to run as normal (there is a subtle hesitation) however when I am at a stop light or in other idling situations, there is a loud rattling sound. I tried to listen to where it appears to be coming from and it sounds as though it is from the front left (passenger side) area under the hood. The past few days, the rattling has died down after driving a couple of miles or so, however it invariably returns. Please advise what it could possibly be and what I can anticipate reasonably to pay for repair. Thanks.