My car is Honda civic ex 2000. Its making constant low noise. This noise started after fuel injector cleaning at a repair center like two months back. After that I took it to dealer to get the regular inspection and they did not find any problem.
Also before the fuel injector cleaning, car used to make a different noise which is not constant but happens when the car speed is between 35 and 50mph. It seems to be coming from exhaust. But I don't where it is coming from exactly.
But after fuel injector cleaning, I could not observe this noise because the low constant noise seems to be dominating.
And ofcourse dealer or other automotive centers did not find any problems. Also freeway mileage dropped like 5 miles currently like 31mph used to be 36-37mph.
Can you suggest any direction to solve these problems?
OK, your noise. I would venture a strong guess that a heat shield on the exhaust is vibrating and/or loose. Check them out. Often hard to detect as they often don't vibrate the same when idling and rev of engine. But put a load on the engine like while it is moving and it comes to life.
Fuel economy, I bet there was a reason to have the injectors cleaned. The injectors feed the plugs and cylinders fuel. Try a new set of plugs and don't forget the air filter.