Identification: Growth in ceiling space b/t basement & main level

I began noticing a "sour" or "sewer" odor in my wash room and smaller bathroom. Next my kitchen sink backs up. These two are most likely unrelated. In looking for a place to run a drain snake I popped the tile ceiling in the basement to check the pvc piping for access. I imagine I've got a moisture issue in my home, possibly a leak, and then this...(reference my attachment).

What in the world is it? Fungi? I can't find any active microbial growth. No sign of mycotoxins or black staining on the wood framing that I can visually identify.

 

I'm no expert, but I'd bet this is called Dead Man's Fingers. Xylaria polymorpha . If you google images some of them will be similar to this, others more fat and blackened. Saprophytic fungi, so growing on old dead wood is right.

 

I suppose I could remove it. But that won't get the source issue which may be a leak from the kitchen sink above? Or at least enough atmospheric moisture there to promote fungi growth? I figured if there was a leak in the sink above, I'd see mold growth on the wet drywall and ceiling tiles in that area but its just not there.