Hayward multiport valve and crackling noise

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

Does the noise eventually go away as you let the system run? When I clean out my pump basket and air gets in the system, my multivalve makes the noise you are describing (it's caused by air trapped in the valve). After awhile the air goes away (dissolves in the water?) and the noise goes away.