Rheem 50 gallon Guardian" gas/electric water heater is run on gas. I just went into the garage and its making a weird noise. It appears that there is a mist coming from the top of the unit into a funnel shaped metal piece. From the mist there are rivlets of water running downthe side into the pan. It is properly draining. What do I do?

Your water heat is at an age that I would recommend replacing the whole unit. That one cannot be too efficient and most likely has sediment built up on the bottom of it pretty bad.

sounds like a corrosion issue if you went into the heater with a copper male adapter or an unlined galvanized or worse a black nipple . replace the connection with a dielectric union that separates the different metals this will also prelong the life of the heater

Troubleshoot?
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

Gene
Water Heater Timers Save Money

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

Copy following link for troubleshooting igniter, and troubleshoot by type of gas control valve:
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#igniter

Add a comment and say what manufacturer appears on label.
Open link above and scroll to top for information about FV lockout.

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

Rheem 50 gallon Pro52-2 has EF .95, which makes it ordinary 240Volt 4500 watt non-simultaneous electric water heater that produces about 21 gallons hot water per hour, with 67 gallon first hour delivery.
Recommend 80 gallon per hour first hour for oversized bathtub.
http://bostonheatingsupply.com/Rheem/Rheem%20Residential%20Electric/Professional/Rheem_ResidentialElectric_Professional%20Spec%20Sheet.pdf

Maintain electric water heater and it will last indefinitely.
http://waterheatertimer.org/How-to-maintain-water-heater.html
http://waterheatertimer.org/9-ways-to-save-with-water-heater.html

Anode rod is located on top in separate port.
Anode keeps tank from rusting.

Year of Rheem water heater manufacture shows 3rd and 4th digit of serial number.

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

21dv50 is discontinued. This is ordinary tank-type 50 gallon gas water heater.
Amazon sells 50 gallon 22V50F1 Rheem water heater for $420 with free shipping ... but who carries the warranty?

Frankly you can get in-store returns, and buy same quality gas water heater at local box store since Rheem makes GE water heaters at home Depot.
Other brands are equally good, as AO Smith makes Kenmore water heaters at Sears and Whirlpool at Lowes.

I prefer the AO Smith because maintenance is easier.
http://waterheatertimer.org/How-to-install-gas-water-heater.html

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

Hi,
Is the noise when the water is running or when the burner is running???

If it is just the water then the noise often is the flow checks inside the tubes going to and from the heater...

If it is the burner, then the noise could be the gas going through the gas valve...a bit of moisture or dirt can sometimes cause noises...usulally will correct its self after a bit of time...no worry...

poping crackling sounds and such are common with mineral builsup in the bottom of the heater....
Flush the heater and get the dirt out....

sizzling noises sometimes happen from condensation dripping onto the burner....gain not a problem...

sometimes the gas properties will cause the gas to make noises when going through the gas orifice into the burner... usually this is air or a LP air mixture known as "citigas" that will burn like natural gas but really isn't and it will make noises such as your are describing...again no problem...

Ultimately the noise you hear is not a problem but can be irritaing if the heater is where you can hear it easily...

Feel free to comment back if you have any more questions...

heatman101

Gas unit? if so check pilot --will go from there-if electric check breaker in electric panel

The model number you gave is for a 50 gallon tank, not 83 gallon.

50 gallon ones are readily available, including the same model..

Stop wondering, replace the thing and your troubles will be over. Your troubles are inside the tank and not worth even giving it another thought. Go for it!