Have a new gas water heater that when I've used hot water I hear a tinnie sound like a drop of water dropped somewhere inside is this normal

Question edited for clarity and add maker.

If this is in normal operation, turn off the gas and water and call a gas registered engineer. If you are turning off the water because you are going on vacation, turn off both the water and the gas. It may be sensing water flow because the pressure has dropped.

It sounds like the thermostat that operated gas valve is failing or the gas valve is bad. This is a repair left to professionals. Now I would price a new heater and install it myself. Repairing older heater is not a good idea, the rest of the heater is old and will fail.

Don't know how old your hot water heater is. They don't last forever. If the tank starts to leak inside the cone it will cause the burner to do this because the water droplets will boil and splatter. Only other thing to cause this is with a cold start up when the tank is full of cold water during high humidity.

The cold water enters the top, but the water is not released into tank at the top. The cold water goes through a "dip tube" This takes the cold water to the bottom of the tank. If you dip tube fails, or breaks, your faucet temperature will slowly drop as you use hot water (vs giving you 60% of tank at full temperature before temperature starts dropping) In normal operation, the cold water is released near bottom of tank, the hot water rises to top, and comes out of the top of the tank.

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Gas or electric?
Electric water heater ... then test for crossover, check for water leak, replace thermostats, test elements
Gas water heater ... test for crossover, check for water leak
http://waterheatertimer.org/Crossover.html

http://waterheatertimer.org/How-to-replace-thermostat-on-electric-water-heater.html

http://waterheatertimer.org/How-to-test-water-heater-element.html

water leak: turn off all taps and put ear against pipe and listen for water leak... check if water meter advances when all water taps are off.

Gene

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Ignoring the pressure drop which often is normal when the burner goes out, note that the pressure may also go up when burner is lit.
After 1 min. - suggest the flame detector needs cleaning. It's situate in the combustion chamber, usually at the rear, and looks like a right angled 1 inch pin above the gas jets. Clean with 240 grit emery cloth and also clean the nearby gas jets with a tooth brush

make sure wiring is correct especially if wired 120 volt read instructions inside panel

1) If water flow stops when tap is off, then Sound of water running: could be factory-installed heat trap inserts or nipples: These things cause noise.
http://waterheatertimer.org/Low-hot-water-pressure.html#trap
http://waterheatertimer.org/9-ways-to-save-with-water-heater.html#heat-trap
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html

2) If sound of water continues when tap is off, then there is a broken pipe or leak somewhere in plumbing system.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

You have clog in hot water line or inside water heater.
Use Brady BTG100 pressure gauge to assist.
http://www.ronshomeandhardware.com/BTG-100-100-PSI-Water-Pressure-Gauge-p/405357.htm

Put gauge on outdoor spigot and then turn on hot water to get baseline.
Put gauge on water heater drain, and then turn on hot water. If pressure stays high, then clog is in hot water nipple or inside pipes after water heater.
If pressure drops, then clog is in cold water nipple, shut off valve above tank, or somewhere in line between main cold water and water heater.
Water heater nipples, shut off to water heater, and elbows are good suspect.
Any galvanized and copper connection is good suspect.

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The only thing you can do is get a couple of unit heaters and point them in the direction of your water heater,and wate for it to un thaw.