i have a 96 civic and when driving the engine makes a humming noise periodically, the outside temp. does not make a difference with the noise. thought it was a bad injector-they are all working. cleaned the IAC, MAP, and throttle body, still makes the sound. i am lost...

 

can you be more specific. also if you could give us a range of speeds in which this humming occurs. it could be a number of things and so your description is a bit too vague. maybe even posting an mp3 of the sound would be even better.

 

I agree. If the noise is metallic rattling or humming under the car, then you may have a loose exhaust heat shield.