Noise coming from slop sink

Question

A new, strange noise is coming from a slop sink that is located next to my washing machine in the basement. The washing machine exhausts into the slop sink and the slop sink drains rather well since I plunged it a few weeks ago.

In the past few days I have been occasionally hearing glunk-glunk noises from the empty slop sink. I am not in the basement much, but I do not hear the noise all the time,

What might be causing this and what might I do about it?

Update: Toilet in basement just overflowed with contents of upstairs toilets. I guess my soil pipe to the street is clogged. I should have paid more attention to the glunk-glunk noise when I heard it a few days ago.

Second Update: Just had the sewer pipe cleaned out. The crew found roots growing in it. (The sewer service company came quickly!)

Answer 1

The "glunk-glunk" is air being pushed or pulled around the water in the trap. Often this indicates a blocked vent pipe. In your situation the upstream plumbing or even the main stack may have been considered a wet vent and be perfectly fine. With the clog at the main near the street, the air pressure inside the pipes is building up from water draining above, and the easiest escape is the sink trap. If possible, I'd still check the pipes to see if there's a vent that should have relieved this pressure, it may need to be cleared from the roof.