1999 Nissan Sunny

Noises problem
1999 Nissan Sunny Two Wheel Drive Automatic 105000 miles

I am hearing a rattling sound coming from my engine that get's louder as I accelerate but it is on and off. I however hear it more whenever I put in gas.
Things to note:
1. The government has forced all gas stations to supply E10 gas.
2. The radiator top had to be changed because of leak (didn't overheat)
3. My coolant bottle crystallized and broke and the coolant was below the minimum mark for a couple of days.(It had a buck start when I move off in traffic until it changed the bottle)
4. My mechanic is saying that only two things can cause " cackling" as he call it --bad gas or overheating. To this date I still have the problem.

PLEASE can you advise me BECAUSE I can't afford to buy another car and I need to sort out this problem as I need my car for work.
January 15, 2010.

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