I have a 1994 Honda Civic EX Coupe Manual 5 spd. There is a rattle or knocking or mettalic gurgle noise whenever I depress the accelerator that immediately goes away when I take my foot off the pedal. It seems to be coming from the engine compartment and happens at all speeds. The sound doesn’t increase or decrease with intensity frequency or loudness with RPM or speed, but is a consistent knocking rattling etc… (kinda sounds like a ball bearing being shook in a tin can) It does seem to be a little louder going up a hill but that’s it. My girlfriends 2000 Echo automatic transmission that has the same problem and I can’t find an answer!
I live in Denver. Use regular gas. And no, I don’t notice any difference if it’s hot or cold.
What is the maintenance record of your Civic and you girlfriend’s Echo?
If they have not been maintained properly, then it is possible that you are both hearing spark knock.
On the other hand, you both might be hearing the sound of loose heat shields.
First, we need detailed information on the odometer mileage and maintenance records of these cars before we can give any guesses that have any real validity. Please don’t give us a general statement such as, “it has been well-maintained”, because upon further probing for information that characterization usually turns out to be inaccurate.
The civic has almost 138k and I bought it from my sister a month ago (she said that noise has been there for years!) It has been maintained by a good family mechanic for the last 7 years and the mechanic has never been able to diagnose the noise. Maintenance included but not limited to Timing belt, fluids, brakes, and an oil pan gasket. Before the car was in our family, the person that owned it hit something on the drivers side, (don’t have any maintenance records) scratching the driver door and denting the rear quarter panel. This has never been repaired as it gives considerable deterrent to anyone wanting to steal the car, and a fair amount of character. The steering is a bit sloppy even after new wheels tires and an alignment, but the car runs and drives well except for this noise.
The 2000 Echo has 95k miles on it and was purchased 5 years ago with approx 40k miles on it. My girlfriends father who is a car nut has performed all the maintenance for it and actually puts 15w-30 synthetic Mobil 1 oil in it. (I just use Max Life Valvoline for the Civic) All fluids and brakes etc, have been done by her dad. This car uses a timing chain, so no timing belt replacement is required.
Does it make sense (if it’s the heat shield) that the noise would only occur when you pressed the accelerator pedal and would immediately stop once the pedal was released?
Also, if it IS a spark knock, why wouldn’t I hear it ALL the time while the engine was running on both cars?
Her father suggested that we were putting in “cheap” gas, so I tried 91 octane. No difference. I then felt a bit stupid after reading Tom and Ray’s take on “high octane gasoline” 
I’ve checked everywhere around both throttle cables in both cars and can’t find anything that could be loosening once the cable is pulled.
Do you have any tests that I should try with both cars to help determine the problem?
Thanks for your help!!!
“Also, if it IS a spark knock, why wouldn’t I hear it ALL the time”
Spark knock tends to happen with acceleration and low to medium RPMs
Engines tend to vibrate more when working hard. It could be a heat shield or a part inside the muffler or cat converter.
Does it rattle if you gradually increase the RPMs with the car in newtral and standing still? If so the mechanic could do this while the car is on a lift to track it down.