This is about to drive me crazy:

The problem:

there is a crackling noise sound coming from the discharge connection of my Hayward SP714 sand filter (244 model). It sounds like a pebble is in there.

What I've done:

taken it apart several times and cleaned; replaced the gasket (glued on type); cleaned or replaced the o rings; replaced the glass bottle and gasket.

Tried closing off skimmers.

I have no water leak on backwash tube now. I did before I replaced the gasket.

Misc:

No water leaks I can see.
No air bubbles in pool that are noticeable.
I just replaced the pump from a 1hp to a 1.5hp and the noise got louder. The 1hp was not as loud and sometimes didn't make the noise. The 1.5hp has constant noise now (more pressure).
The pipes are 1 1/2 inch.
New sand this year but it was doing same before I changed it.
Pools seems to circulate fine.

Any suggestions? Thanks in advance. Jed