I've noticed that when I accelerate hard on an exit ramp heading to work (it's uphill) I can hear something like water gurgling. I'm thinking heater core, but I'm not losing antifreeze nor am I leaking it anywhere.
It's hard to pinpoint where the noise is coming from, but it sounds like somewhere in front of me as best as I can tell. Could it be window washer fluid?

 

Check the coolant level. Check to see if the passenger side carpet is wet. Do the windows fog up ? Is there a sweet smell inside the cab? Those last two will help determine if the Htr core is leaking. If none of the above, bleed the air out of the cooling system and the 'gurgling noise' should go away.

 

I have a 95 and an 04 Blazer,and they both make this same noise.Its like I can hear the water going thru the heater core.No leaks in either,and heaters both work fine.Drives me nuts.

 

I have the same thing, but I think mine is actually a vacuum leak.

 

Mine has done the exact same thing, and has done it every time I've drained and refilled the cooling system for whatever reason (be it maintenance, flush, whatever). I never can seem to burp all the air out of the system... Air gets trapped in the heater core and causes the noise. Usually it goes away within a couple weeks, sometimes lasts a couple months, but it's harmless. When it does eventually stop, just check your coolant level; the air is gone from the heater core and it usually gets trapped in the radiator at that point, so pop the cap off and top off with antifreeze.

 

Try parking with the nose uphill or on jack stands when burping, the radiator cap being higher than the heater core helps the air escape when burping the system