HELP! Clicking Noise in Hot Air Heating Vent

[ineedhelp]

There's a very regular clicking noise (sounds like a ticking clock, or water dripping) that I can hear from the vents in my house. When the hot air's blowing, I don't hear the clicking sounds, but when the hot air stops blowing, the clicking noise starts. Does anyone out there have any ideas as to what it could be, and how to fix it?

P.S. I have a gas furnace heating system.

[HayZee518]

if they are bare bones galvanized trunk lines, the ducts heat up and expand when heated air goes through them. when the burner shuts down, the trunk lines contract because of cooling off and the noise you hear is the trunk lines cooling down.

[ineedhelp]

Is the clicking noise a problem that I need to have fixed right away? In other words, does clicking = something wrong with the system?

Is there any way to stop the noise? Or reduce it? It sounds like dripping water.

[HayZee518]

the clicking is just the joints of the trunk lines moving. the trunk lines are held together by "S" cleats and "drives." these are just sheet metal pieces fabricated to hold everything together. The most effected parts is the trunk line(s) nearest to the furnace. the long trunk lines should have been cross creased during their manufacturing to keep the sheet metal from flexing and causing pops. the "drives" fit over a quarter inch bend bent back over itself to form a hook. the drives are like a flattened out "U" shape of sheet metal. this "drive" is hammered over two "hooks" of two pieces of duct work. if the srive is loose it may expand more then the rest. Take a piece of gray duct tape and tape over the drives. this might lessen the clicking noises.

[ineedhelp]

I had a guy come over to check it out and his *guess* was that the noise could be coming from a blockage somewhere along the airflow passage. He also said something about the noise coming from "condensation" but I didn't understand. Did he know what he was talking about or just BSing me?

[HayZee518]

if the air passage is very warm and the outside of the trunk line is very cold, there is a good chance of developing moisture, but this would be on the outside of the trunk line NOT inside. as far as a blockage, if your system has "turning vanes" inside of a sweeping elbow, maybe some of the sheet metal used to form the "turning vanes" is loose making a ticking noise.

[cajin]

I have a similar but a little different problem. The noise is not only clicking and water dripping noise. Sometimes it is like the noise that you push a thin metal sheet and it pop back. This noise comes from all through out the home - but I guess it is from the ducts. And it is also loud occasionally. I have been observing this problem for 3 nights since I moved in this home. I already found one duct which has loud noise. I really want this problem get fixed because it affect my sleeping a lot. Can you give any advice?

[HayZee518]

at this stage it is a little late! whoever made up the ducts should have cross creased the long trunk lines. what cross creasing means is when the duct was made on a press brake, the side pieces of the duct are placed in the brake corner to corner and a slight crease is made, then flipped around again corner to corner and creased again. rhis gives the look of a large X on both sides of the trunk line. air going through the trunk line with any force expands out the sides of the trunk. without cross creasing the sides "pop" out and then "pop" back in giving you that noise.

[cajin]

So do you mean there is no way to fix it? Or it is very expensive to fix it? What kind of work has to be done to fix it? The noise is too loud, I hope to reduce it at least. For example, sometimes, the noise is as lound as a book dropping from table to floor.

[HayZee518]

yeah it can be a pain in the ears! if you can find the section that is causing the pop, you may be able to fix it by using a long piece of sheet metal. cut a piece about 1 1/2 inches wide BY about three inches longer than the duct. use a sheet metal screw and fasten one end at the end of the trunk line. then take a block of wood, 2 inches square and place it in the middle under the strip and the duct and screw the other end into the duct. what you're trying to do is create tension between the block of wood and the trunk line to keep the trunk from popping whenever air goes through it. you may be able to lessen the popping noise by unscrewing the hanger on the trunk and shoving it nearer or further away from you and re-fastening the hanger.