The CLUNK (in ductwork) that just won't go away ...

[Puddin' Man]

This is just a shot in the dark. The problem (described below) persists.

I had removed the register, added new rope caulk to seal around perimeter, and replaced register. And it worked: the CLUNK went away.

When it came back (with a vengeance)last week, I pulled the register and the CLUNK immediately went away. That's where it stands now.

The register fastens to the plaster and ductwork with 2 screws. I checked very carefully for loose ductwork where the register fastens. Nothing loose.

I'm at a loss to figger out what the difference is (other than the CLUNK) between having the register mounted and having it removed.

Any ideas??

Thx, P

I chased this. The CLUNK was actually in the bedroom vent. When I >removed the register, it went away for a while. It's come back >but it's so infrequent it's a PITA to trace (twice a week >or thereabouts). > >Thanks to aemeijers for advice. It's probably in the wall: >I'll find it someday. > > P > >> >>Greetings, >> >>Little brick bungalow in the midwest US, built in 1954, poured-concrete >>foundation. Standard forced-air HVAC, galvanized duct-work. >> >>New Heil furnace/AC in 03-2010. For years, in the winter, t-stat will >>call for heat, and about 20 seconds after the blower kicks in, I hear >>a CLUNK from the area of the kitchen vent, kinda like someone smacked the >>duct with a board. >> >>Back in the '80's I cut a hole in the duct, added a vent for a basement >>bedroom near the kitchen duct. Doubt that is connected. Can hardly hear the >>CLUNK in the basement. >> >>I'm guessing the ductwork for the kitchen vent is somehow stressed-out, >>pops as it warms up. It is inside a partition wall between the kit. >>and a bedroom. Old-style plaster on steel lath. >> >>What commonly makes galvanized ductwork over-stressed? How can one >>unstress it? >> >> >> Thx, >> P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."

[Vic Smith]

Probably just a coincidence since the clunk really didn't go way. Maybe the temp changed. Even barometric pressure.

My guess is without the register there's less pressure. I get those clunks now and then. No telling when they'll happen. Just the sheet metal flexing. Could be many feet away from the register but that's where you hear it. If you can find where it's actually flexing and it's accessible a single wrap of duct tape might fix it. It never bothers me when I hear it. Just sheet metal being itself. Wife used to get all excited about it until I told her to just shut up about it because it'll make the ghosts mad. Now she doesn't mention it either.

--Vic

[Puddin' Man]

No. It was 99% consistent and replicable with register in place. Haven't heard it since removing.

Obviously.

No. It's not random. Happens about 50 seconds after the blower kicks in.

It's inside the wall. Plaster on steel lath.

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."

[Ashton Crusher]

I had a noisy run of duct and I quieted it by putting a long piece (about 15') of PVC in it so that the PVC bowed against the duct work to push it out and keep it from flexing. Hard to explain but basically got the two ends of the piece to "anchor" against something forcing the middle to bow out against the duct.

[Vic Smith]

You just said above after you caulked the register "the clunk went away." THAT was the coincidence. Clunk is back now, right? If it's NOT a coincidence then it was the caulking and refitting of the register that stopped the clunking at least temporarily. You decide what's true.

If you know the damn answer why are you asking the question?

If you're sure of the sound's location there's 4 options I can think of right off.

1. Try a register with less restriction.
2. If you can reach the spot from the register devise something that can expand the duct so it doesn't pop. A threaded rod or spring-loaded something. Rubber ends to grip like some expanding shower rods. Attach a wire in case you drop it, then attach the wire to the register with slack in case it wants to drop itself late . Hope nothing whistles.
3. Cut away enough plaster/last on both sides of the duct to wedge and compress it, then wire up new screen and replaster. Hope the popping is on the wall sides and not the short sides.
4. Live with the clunking. That's what I'd do.

--Vic

[Rick]

Loose damper door in the ductwork...

[trader4]

First thing I'd be sure of is that it's in the duct inside the wall and not in say a main supply duct in the basement right before the branch off, etc. If it indeed is inside the wall, then I like the suggestion of getting a piece of PVC pipe, maybe 1/2 or 3/4" and try shoving a length of it down the duct so that it might wind up situated so that it prevents the duct from flexing at the right spot.

[Limp Arbor]

quoted text -

In my house my return vent sucks in on startup like if you put you finger on the bottom of a straw and sucked the straw. It bangs like hell and you can hear it throughtout the whole house.

Barely noticeable when the basement door is open.

non-existent with a return grill removed.

Loudest with a new air filter and gradually gets quieter until I replace the filter 30 days later.

You have to pay close attention and do a process of elimination. If it truly does only occur with the register installed it is probably as posted the resistance in the system causing something to bang.

[DerbyDad03]

re: No. It's not random. Happens about 50 seconds after the blower kicks in.

Hook up a timer relay to turn the blower off at 49 seconds and then back on at 51.

[Puddin' Man]

Interesting.

The offending register is 1 of 5 identical units in the little house. Its also the next-to-the-farthest from the furnace.

Thx, P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."

[Puddin' Man]

Do you think thats 100% of the answer?

...

I probably will, too. But there's folks out there with vastly more experience than I. They might know something that we don't.

Told ya it was a shot-in-the-dark. :-)

P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."