Have had a bad odor for a few days under bathroom sink. Drain is clean and water runs smoothly. Today I disconnected the pipe under the sink and the smell seems to have disappeared. What would cause this?

It could be number of things ranging from spilled water to toiletry stored under the sink. Hard to speculate now when odor is gone. Milo

If it smelled like sewer, it could have been that the p trap wasn't functioning correctly. I'm not a plumber, and I wasn't there ofc, but I know that sometimes if it doesn't hold water like it should it might smell badly.