The rain cap seems the right size to my untrained eye. Did the roofing crew install the storm collar and/or flashing incorrectly?

 

My thoughts as well, most likely the flashing. Might be fixable with caulk, might need renewed.

 

A reputable roofing company would likely repair their mistake for nothing.

 

And what noise would you hear as the metal expands and contracts?

 

The first thing that I suggest is to determine is if the dripping is inside or outside of the chimney (or remotely possibly within the chimney itself, since it is of double-wall construction). An inspection in the attic while the sound is happening should allow you to eliminate the “outside of the chimney” possibility. Keep in mind that water coming down inside the chimney would encounter a baffle at the top of the firebox that would quite likely redirect it away from view, like behind the firebricks visible through the door.

I also suggest to inspect the attachment points of the braces to the chimney. They are two locations that, if not sealed properly, will allow rain to enter the chimney.

Chris

 

We had exactly the same problem. I went outside during the last good blustery storm and watched rain drops fall from the top flue securing bracket near the roof onto the flue/wall securing bracket at flue entry to the house. It was like a drum. A small deflector plate sorted it out.

 

I don't see any storm collar. You may not need one if smoke pipe goes up and outside of the house. But if it goes through the roof, Imo, you should have one. Can't really tell by picture, but looks like it runs on outside of house up through the soffit so you wouldn't need it.

But as the above poster states, he put on a piece of metal deflector and it solved the issue. That's basically what a storm collar does also. Available at any box store.

This is a utube video of a storm collar installed in an incorrect position on the smoke pipe. Just as an example only.