Question about pool rail

[shiyang100]

We got some rain yesterday, so this morning I spent some time cleaning the pool deck, getting rid of pine needles and leaves....

Interesting I heard some water moving sound inside of pool rail. So I took off the cover at the bottom, and I noticed the water bubbled up. It stops after 30 seconds. Anyone has idea why this happens. I looked around the pool, could not think of any underground pipe.

 

[kimkats]

Rain water collecting in it? Did you try to get it out?

 

[shiyang100]

No, I didn't get any rain water out. Just feel so strange when you heard water flowing inside the handrail and saw water bubbled up at the bottom.