This morning , heard our water heater making "popping" sounds. Online, found that a possible solution is, flush the sediment out of the tank. My problem is, I can't for the life of me find the drain ****. Unless it's on the bottom side of the water heater. All I can find is a brass valve on top. The water heater is about 2" off of the floor and in a corner. Is it possible that I'm just missing it somehow? It's an old one, Rheem model #35-30, 30 gallon capacity.

I'm not sure what you mean by "gurgles when refilling." If you mean that it is making noise when heating the water, that is usually a sign that sediment has built up in the bottom of the tank. This results in the surface of the tank bottom to overheat and the sound you hear is the water flashing to steam. This usually results in tank failure as the glass lining will crack an the tank will rust out. If it's not too late you could drain and flush the tank to try to remove the sediment but if has hardened to a solid mass it won't come out.

Usually nothing to worry about. Sometimes sediment in the bottom of the tank will cause small air pocket to form and pop. The cure is to drain and flush the tank.

Here is a pic on how to do it. And a link to the AO website manual

The sediment that can build up in the bottom of a water heater can actually harden the popping sound your hearing is from the water that is trapped under the build up. when your heater fires the water under that build up has no where to go so it turns to steam so the popping sound is that steam bursting through the build up. If flushing it didn't help the only way to stop it would be to get a new heater

Check and see if the cold water has been plumbed to the 'c' on the heater, the hot to the 'h', and the relief valve somewhere else, usually on the side. Maybe the plumber cheated somewhere to make installation easy.

Popping sound is caused by sediment built up in bottom of tank: air bubbles get trapped when heating starts, and then they crackle, rumble etc when free.
Clean out sediment:
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html
http://waterheatertimer.org/pdf/How-to-descale-water-heater.pdf
The steps vary by type of water heater, gas or electric

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

zdriscoll-

All tank water heaters make some amount noise, clicking and "snapping" sounds, particularly after much of the hot water in tank has been used (like after a long shower) and has been replaced by cold water that is being heated vigorously.

If the noises are accompanied by poor or erratic performance, or obviously if something malfunctions, you may require the services of a repair connection.

Hope this helps.

Regards,

DIYpro

GE is made by Rheem, but the market is always changing. Rheem-based serial number shows tank was made in 1990.
Tank will last as long as anode rod(s) protects steel tank from rusting.
If your tank has two anode rods, then tanks lasts longer.
That's how companies determine if water heater is '6-year' or '12-year.'
I don't have manual for your product to say if you have 12 year tank. Side of tank might have information blurb besides mandatory label that shows serial number.
You can update your water heater by replacing anode rod(s) assuming they can be loosened and removed after this number of years, which is a big IF with old heaters. Your plumber might have impact wrench he uses to see if anode can come out.
http://waterheatertimer.org/Replace-anode-rod.html
http://waterheatertimer.org/Leaking-water-heater.html

If the water heater is making gurgling rumbling and/or crackling sounds then tank has sediment build-up.
You can also get a baseline of rust by flushing tank and watching if water is very rusty.
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html
http://waterheatertimer.org/Water-heater-will-not-drain.html

If you flush tank regularly, and inspect anode every 1-3 years, a tank will last many years longer than manufacturer's label.
http://waterheatertimer.org/Water-heater-manufacturers.html

You posted under electric water heater.

1) Gas or electric, the noise is from sediment build-up inside tank.
Once sediment builds up, the only way to solve problem is to clean the tank out.

2) To restore full efficiency to electric water heater and stop the noise, clean the tank:
http://waterheatertimer.org/How-to-clean-sediment-out-of-electric-water-heater.html
3) To clean gas water heater is more difficult and less successful:
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html

4) To prevent sediment problem, flush water heater each 6 months before sediment can build up.
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html#flushelectric

5) Other things to know for water heater maintenance.
http://waterheatertimer.org/Replace-anode-rod.html
http://waterheatertimer.org/9-ways-to-save-with-water-heater.html

sediment build up is usually causes thumping and noises from tank. it needs flushed out. models, where the heat source is beneath the tank. The burner heats the water under the sediment, leading to a build of steam. The steam finally escapes as bubbles, which can cause the sounds.

have a good day !

Usually when a tank is making noise, it means the tank needs to be cleaned out or flushed.
I wrote a page with diagrams showing how to clean out a tank, and how to flush the tank.
Page shows gas and electric water heaters.
See if this helps:
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html