1997 Chevy Blazer Swishing noise in dashboard

Hello,

My car has been making a swishing sound in the dashboard, behind the center console. It sounds like water moving around when I drove, I notice it the most when stopped. The car has not been running that great either, I was told it needs a tune up and just recently bought new spark plug wires, have yet to put them in. Also, the coolant is very low, I have to keep filling it up because it becomes almost empty. Could the water from that be leaking someplace else. How big of a fix/problem is this? I recently have had to replace ignition switch and my entire fuel pump assembly. Please help! Thank You!