1)
Why does it say "Koli El Hashem Ez'ak Koli El Hashem Eschanan"?
1.
Radak: I will scream to him amidst my affliction; the matter is repeated.
2.
Malbim: While in the cave, he feared to scream aloud, lest the enemies hear. I can scream to Hashem without fear. I cannot supplicate at length even quietly, for this would inform that someone is in the cave 1 . However, I can supplicate to Hashem audibly, and not fear.
1
It seems that he discusses screaming to Sha'ul, or supplicating to him at length. (PF)