The gas making the popping noise is hydrogen.
If by "popping noise" you mean backfire, it could be crossed ignition wires, or some sort of misfire.
Could be one of a number of things, as it could be in any vehicle.
Rice Krispies IHTH :)
Just grease the fittings... It makes all the difference
Maybe a stone stuck in the tire tread.
i have a jonway 49 cc scooter. it has been bored out but i dont know how much. but whenever i go down hill or reach 60km/hr it makes a popping noise like is is backfireing
could be a contant velocity joint
Replace the speakers. Adjust the Fade/Balance and listen to find which speaker is popping. The popping noise is most likely from a broken cone in the speaker
you probably need a cv joint
The popping noise in your water heater could be due to sediment buildup at the bottom of the tank. As water is heated, the minerals in it can form deposits that create air pockets. When these air pockets burst, they can create a popping sound. Flushing the tank to remove sediment buildup may help reduce the popping noise.
try replacing your coolant temp/sensor $5.00