Rattle in vent system behind wall after gas company furnace maintenance

[woolyninja]

This past November I had the gas company come out to perform maintenance (cleaning, etc) on the furnace and shortly thereafter whenever the furnace would run there was a rattling/vibration sound coming from the vent in the wall/ceiling in the room next to the furnace. Had the gas company back out to look at it but they couldn't figure it out. Then a couple months later it stopped.

I assumed it was some loose debris that due to the improved airflow from the cleaned up furnace was being rattled around, however, now we just turned the A/C on for the first time and once again the rattling noise has started back up?

Does anyone have any ideas as to what this might be?

[duckman06]

While this could be a number of things. At first I was thinking maybe the vent pipe had came apart or is coming apart causing the nosie but after reason your post further and sound went away then started back once ac was turned on is werid?

Are you sure it's not the furance itself rattling? Regardless if gas company can't figure out, I would call your hvac service provider and have then out to look at the system and see if they can make since of the noise and offer solutions to correct.

[woolyninja]

It doesn't seem to be coming from the furnace itself. If I go in that room I can hardly hear the rattling (or hear it at all really). They did take the whole thing apart when they were here to "clean" it, etc so I suppose its possible there's something loose in there.

[BNME8EZ]

Check the damper in the registers, it may not be the one in that room. I had one that they could hear in the Dinning room but the register was in the basement.

[woolyninja]

I'll check them all out and see what I can find.

[mechanical'al]

possibly check the balancing damper in that run or others near it ??? Theirs a wing nut to secure in place it may have come loose????

[woolyninja]

I think you're on to something with the balancing damper - even though its nowhere near the spot of the noise if I mess with that area around that damper the noise stops temporarily. However the wing nut is crazy tight so i'm thinking there may be an issue with the entire assembly. I'll look into it more this weekend. Thanks for the suggestions!

[mechanical'al]

generally on the back (inside) theres a cup shape that may be loose ,though strange still sounds like possiblity of some kind of a restricted air flow

[precision hvac]

Why is the Gas Co disassembling your furnace?

[woolyninja]

I had them do standard maintenance and apparently taking apart the entire furnace and cleaning each part was something they did? No idea really, but it actually seems to work better (more air being pushed around the house, etc).

And as a final follow up... I wanted to wait a few days to be sure. But I was able to tighten that balancing damper I had mentioned previously (which is nowhere near where the noise seemed to be coming from) and haven't heard the rattle since.

Thank you all so much for the suggestions!