Is it soundproofing? Or is it something more?

I live in a one-level condo with a closet that holds both the gas furnace and water heater.

2 things.
1. When the gas furnace turns on, it sounds like the 4-horseman coming from the heavens for armageddon. It is the fan! What do I have to do quiet that fan? Would WD-40 sprayed into the fan(s) do anything?

2. The water heater turns on and off every 5 seconds or so. On..5 seconds...off 5 seconds ...etc...etc.

If these two things are normal ..how do I sound proof that closet?? Any suggestions would be appreciated.

What you describe is typical of an older and/or poorly maintained furnace. I'd tear into it and work my way back out while inspecting, tightening, aligning, adjusting, balancing and oiling everything.
The water heater sounds like it might be electric with a bad or misadjusted thermostat and/or bad heating element. A quick run down of the typical troubleshooting ladder should solve this issue.
You most likely don't want to attempt to sound proof the closet as some air is required by both appliances.

Welcome Corganer:
WD-40 is a wonderful product with many good uses; however, your furnace blower motor is not one of them or any other motor. WD-40 has some sort of silicone base and dries out quickly in a motor leaving it to burn out the bushings or bearings. I use the Zoom Spout oiler for motors, it can be picked up at heating and airconditoning shops, sewing shops or big box stores.

Having a gas furnace leads me to believe you also have a gas water heater which could be heard when it kicks on and off. This short cycling is a big waste of energy and is probably caused by the thermostat. Try turning the temperature down 5-10*. You may also need to drain the water heater down some to get rid of scale in the bottom. If you hear your water heater rumbling when it is heating, it is the water boiling and bubbling up through the sediment. The only other thing I can think of that would affect the temp of the water and cause short cycling is a dip tube that has broken loose or disintergrated. The dip tube is on the cold water side and carries the coldest water to the bottom to be heated, while the hot water rises and is used first while the wh is heating more at the bottom.

You can find the dip tube by taking the fittings loose on the cold side, sticking a finger in the hole, bend the finger and pull. You should come up with a 3' long tube of plastic or copper. If there is none you can use a 3' piece of 3/4" copper with a flare on one end (that's what keeps it from falling down in the tank).
Glenn

Thank you for the replies.

What do you mean by lowering the thermostat 5-10 degrees? What will that do? Reset something?

Shots in the dark and temporary fixes are what causes these problems. The easiest way is seldom the correct way. A broken dip tube shouldn't cause an idling hot water heater cycling. Is this water heater gas or electric. My guess is electric with bad T-stat(s) and/or heating element. Suck it up, break it down and reassemble as described earlier. And please use the Zoom oil that glennjanie mentioned.

It is actually a gas water heater. It has stopped for the time being with the cycling ..which may tell me it is the thermostat. IF it is the thermostat (and i will check everything else as well) ...Do I just check the wiring to the thermostat?

kok328...I am certainly going to get my hands dirty on that furnace blower (and clean everything in the entire unit since previous owners neglected). tighten...inspect..oil. I think it is loud because it is yelling at someone to give it a check-up!

Also, and this is going to make me sound dumb, but this is why I am asking experts .... in the gas water heater ...the pilot light flame is burning a small metal piece(?) directly above. What is that?

I believe that small piece of metal is the flame sensor. This tells the system that it's OK to flow the gas.
Short cycling on a gas water heater would have to be the T-stat. I remain that a broken dip tube causes short cycles on an idling heater.