Do we need to shut off the gas or pilot light when draining out sediment on our gas water heater?

no info generic answer --check thermocouple --and safety switches

Make sure your gas is not shut off.
Do you have any other gas appliances that are working?

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gregg_27a4d257e54e7920

you didn't specify whether it was electric or gas, so i'll assume it's gas. Clean or replace the thermocouple that the pilot light heats. Yes it could be the thermostat as well.

the tank needs flushed out ! heres how. Water heater manufacturers recommend flushing sediment from your storage type water heater periodically.
If your water heater is gas, set the gas valve to "Pilot" to prevent the burners from coming on while you are flushing it. If your heater is electric be sure to turn off the circuit breakers. With an electric water heater, if the water level drops below the heating elements and the thermostat turns the elements on, the heating elements will probably burn out quite rapidly. Connect a garden hose to the drain valve at the bottom of the tank, Close the shut off valve on the cold inlet to the water heater. open the temperature/pressure relief valve at the top of the tank by lifting the lever. Leave the valve open. Open the drain valve at the bottom of the heater allowing the water to flow out through the garden hose. when the water is clear your finished. close pressure relief valve on top of tank and turn water back on.
Open a hot water faucet in your house, and let it run until no air bubbles come out.

Turn the heater back on, and with gas units re-light the pilot light if necessary. good-day !

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Why did water heater turn off?
If water heater was exposed to flammable vapors like gasoline, paint thinner, paint, leaking gas line, etc, then the 'single use gas shut off' might have tripped.
If water heater is older and the burner parts never cleaned, then combustion chamber can experience overheating, and that can trigger 'single use shut off.'

Instructions for lighting water heater should be printed on side of heater.
Follow the instructions and see if water heater will light.
Then check if flame is clear blue. If flame is yellow-orange, then burner parts need to be cleaned.
If water heater will not light, then combustion parts may need to be cleaned, and air intake cleaned, and 'single use shut off' could also be tripped.

Also possible that gas control valve thermostat is bad.

Open following link to help identify gas valve and see illustrations and read information about cleaning combustion parts:
http://Waterheatertimer.org/How-to-install-gas-water-heater.html#troubleshoot
http://waterheatertimer.org/How-to-adjust-water-heater-temperature.html#intelli

Problem is not clear.
Is water heater clogged and not draining?
What kind of shut off is normally located down near drain valve on electric water heater?
If you have gas heater, you can normally just rotate knob to pilot to shut off burner.
If you are draining electric water heater, normally you turn off circuit breaker, attach garden hose to drain valve, open drain valve by turning counterclockwise, open TP valve or open bathtub faucet, and then water drains out.

Open following links for illustrations.
http://waterheatertimer.org/Water-heater-will-not-drain.html
http://waterheatertimer.org/How-to-replace-water-heater-drain-valve.html
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html

I believe 640 is typical tank-type atmospheric-vented gas water heater.
Gas water heater problems can get complicated. New heater sells for $350 at local box store.
http://waterheatertimer.org/How-to-install-gas-water-heater.html

If thermostat is not controlling temperature accurately, then (1) gas control needs replacement (2) water heater has sediment build-up (3) combustion and burner parts need cleaning. (4) All three things above, plus additional causes such as bad venting or not enough combustion air.

Usually recommended that plumber replace gas control valve thermostat:
See typical tank-type thermostats:
http://waterheatertimer.org/images/Typical-gas-valve-500.jpg
http://waterheatertimer.org/How-to-adjust-temperature-on-water-heater.html

Clean sediment out of tank:
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html

Clean combustion chamber and burner parts and troublehoot venting and air supply:
http://waterheatertimer.org/How-to-install-gas-water-heater.html#troubleshoot
http://waterheatertimer.org/images/Clean-burner-300.jpg
http://waterheatertimer.org/pdf/Bosch_Ventilating_tight_houses.pdf

Valve is not identified.
Cold water shut-off valve, TP valve, check valve, mixing valve, drain valve are the usual suspects associated with electric water heater.
Gas water heater has additional valves: gas shut off valve and gas control valve thermostat.
Check valve, TP valve and mixing valve probably need replacement.
If drain valve is leaking, put garden hose cap over end.
Shut off valve probably has a bit of blockage, or is not completely open. Try closing and then opening shut-off valve all the way, and if problem persists, replace or clean out valve.

What kind of noise? Are you sure the noise is from a valve or is it inside the tank caused by sediment build-up inside of tank?

http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html
http://waterheatertimer.org/Low-hot-water-pressure.html
http://waterheatertimer.org/How-to-replace-TP-valve.html
http://waterheatertimer.org/images/Water-heater-with-mixing-valve-300.jpg

The thermostat probe on most residential water heaters is part of the gas valve. The thermostat is a non replaceable part of the gas vale and if your t-stat is bad you will need to replace the gas valve also.
This is generally not a very hard job just start off by shutting gas supply valve to off position.Disconnect main gas line to burner,line to pilot light, and thermocouple from gas valve. Remove pipe fitting from gas valve and use large pipe wrench to loosen gas valve.
Before you loosen gas valve you will need to shut water supply off and drain water from tank.MOST WATER HEATER GAS VALVES ARE PRETTY STANDARD ITEMS AVAILABLE AT MOST HARDWARE STORES. Just make sure you purchase valve for the type of fuel you have,such as l.p. or natural gas.Remove gas valve by turning counterclockwise. Use teflon tape or pipe joint compound on all threaded connections for reassembly. Hook up gas line,burner supply line,pilot and thermocouple lines. Refill tank and check and check for leaks. Light pilot and turn gas control to on. Set to desired heat setting . Also check all gas fitting for leaks. Good luck. Thanks

Begin by turning off the gas at the tank and at the valve near the tank. CAUTION: Do not proceed any further if you do not know how to relight the gas pilot!
2) Turn off the COLD water supply to the tank.
3) Attach a garden hose to the drain valve at the bottom of the tank. Run the hose to a convenient drain location. Be careful if you use a real cheapy garden hose... some of these become very soft when hot water runs through them, and may leak! If you don't have a drain in the basement floor or suitable sump hole, you have my sympathies... this drain-down can take a while with a bucket! Oh... and be careful if you use a soft plastic bucket. It can also soften from the heated water so don't overfill it or burn yourself!
4) Open up the hot water side of any faucet. Open up the drain valve on the tank and allow it to empty. Miller time. That is, unless you don't have a sump...
NOTE: If the drain valve clogs, turn on the cold water supply to the tank to use water pressure to "blast" through the clog.
5) When the tank is empty, shut off the drain valve and turn on the cold water. This will loosen up more sediment in the tank through the churning action of the cold water in the tank. Let the tank fill partially and drain it again. In fact, if you find that the sediment starts to clog the drain valve, turn on the cold water supply to the tank, which will help loosen the sediment and blast it out.
If you have extreme amounts of sediment, you may have to repeat this procedure a few more times. Look at the drain water... if it is running clear, you are done. Shut off the drain valve, open the cold water supply and allow the tank to fill. Once water comes out of the hot water faucet, the tank is full and your task is done! Now, you can turn the electricity or gas back on to heat the water.
How frequently to clean the sediment from your tank...
This depends on the source and purity of your water supply. Some pros recommend doing it annually, some every few years. I would recommend doing a partial drain down annually if you find any sediment in the tank, otherwise every couple of years.
Remember that with an electric water heater, you must turn the power off! Even a partial drain down may expose the upper heating element to the air and permanently damage it!