I have a musty smell coming from under a bathroom sink. Really not sure how to get rid of it. There is no apparent leak. No evidence of water damage. The sink is a 'bowl' type that sits on top of the counter and does not have an overflow. Any suggestions of how to get rid of it is would be appreciated.

Does it appear to be coming from inside the wall where the drain stub comes out? Maybe the drain vent pipe was not glued in place and it came apart, letting sewer gas escape.

A musty smell usually comes from wetness in my experience. Maybe you could leave the cabinet doors open for a few days to see if it goes away.

musty usually means wet or damp, the counter is probably particle board under the shiney surface and the floor is probably particle board under the finished floor if the house was built in the 70-80s, maybe the floor is getting a few drops of water somehow everytime the fauset is turned on.
I once had a leak that we didn't know about for many months til the floor started turning spongy under us, the particle board had turned to saw dust out five ft from the sink., the tiny leak that we couldn't fing was being absorbed by the particle bd, my wife complained about the smell for months, but I never smelled it and told her she was dreaming til it was too late.

Thanks for the input. It is bad again tonight. I will get under there again and try to check connections and maybe drill a hole or two to see what is behind the wall.

Wanted to update- four years ago we replaced two sinks with a single one in his bathroom. The plumber piped the new sink, in the middle, over to the right drain....leaving the left drain line in place and open...I presume that sewer fumes are being pushed out the left drain line and into the room. I stuffed a wet rag into it for tonight, and I hope that is the problem....onl thing I still can't figure out, if this is the problem, is why we had not had this problem long ao since this configuration has been n place like this for over four years.

An actual plumber did that?



Was the trap still in place, maybe there was still water in there sealing the fumes, but I would think it would have evaporated within a year.
Maybe there was already a rag stuffed in there, and it moved and allowed an opening.

I can't think of ANY actual plumber that would ake a mistake like this. Possible he capped it, and the cap recently fell off?

Regardless, that open drain needs to be sealed closed (capped).

The left drain is probably "T" ed into the tailpiece above the trap of the right drain, still you'd expect he'd stub it off and cap it. A clog would make a mess.

I agree, it;'s hard to believe a plumber would do that.

Not the way this reads, "...plumber piped the new sink, in the middle, over to the right drain....leaving the left drain line in place and open..."

But regardless. There seems to be an open, UN-trapped pipe that needs to be sealed off.