If the pump quiets down and pressure goes back to normal when you switch to full skimmer then it sounds like you already know what and about where the problem is. Low pressure can also be caused by a gunked up impeller but that would cause low pressure in both paths. The noise probably is cavitation which happens when you have high vacuum areas that cause local boiling. With a blocked suction line the vacuum increases and this could cause cavitation around the impeller or even just pulling air out of solution in the suction line.
Not even thinking about pools in this neck of the woods. Got about 30" of snow a couple weeks ago and under the slush that's left there is a solid block of ice. Bah!
Al