loud knocking noise on 2002 Mitsubishi Eclipse

my car has 150,000+ miles on it. I have performed all maintenance required for that high mileage. upon start (but not EVERY time) the car makes a very loud knocking noise that continues sometimes all day. The noise occurs at idle and at accelaration as well.(altho when driving at higher speeds its harder to hear) The noise does not occur all the time-but its now increased in frequency. I drive in commute traffic (sf bay area). Maybe unrelated-but the check engine light goes on and off. I have recently switched fuel grades and that seems to have helped that issue. Any clues?

by in Benicia, CA on December 27, 2010
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1 answer 2 comments
ANSWER by , December 27, 2010
A knock is bad. Something is not right and it should be looked at before it gets any worse. Let me know if Milt's can help. We're in Vallejo. Good luck.
COMMENT by , December 27, 2010
Thanks Hal. Would it cost me anything for the diagnosis? I work in the city-every day-so having my car is vital. Are you swamped this time of year? Kirsten
COMMENT by , December 27, 2010
It's not that bad right now. Mainly servicing cars home for christmas break. Call Adrian at the shop (707)643-7548. If he can tell you something without putting a technician on it or putting the vehicle on one of the lifts there will be no charge. We're here to help. Happy holidays.