With isopropyl alcohol, a syringe and a small paintbrush you can do the trick.
Just squirt some alcohol onto the speaker so it penetrates the speaker. Put on some loud music and let it play while adding more alcohol.
Repeat this for like 10 times and in the meantime gently tap the speaker grill with the brush so the small hairs get inside the speaker and loosen the glue sticking to the grill.
After like 10 minutes hold your phone firmly with the screen downwards and tap it against your other hand so the isopropyl with the dissolved loca can come out.
Repeat this until the crackling is gone.
Did it twice this way on my s9 plus and works fine.