I seem to be leaking coolant slowly and I have to fill it up every 3 weeks or so?? Where is a common place coolant leaks from? The leak is so slow I can't seem to find it.

 

That is pretty slow. You're adding to the reservoir, or the rad?
No puddles under the car?

Squeeze your hoses to check if any are swollen and weeping. Check for wet spots near the waterneck, intake manifold..... And of course the rad cap itself.

I'd just run a can of stop leak in there and be done with it

 

Im guessing maybe its the intake manifold?? because before I noticed the leak I started to hear this whining noise(unsure of where its coming from in the engine bay) Would the intake manifold make a noise like that if it was leaking??

 

Most of the time a slow leak is nothing major. A vacuum leak could make a noise if it was big enough but it's more of a whistle. Your idle would be suffering if that was the case. If you have a noise my thoughts are that it is pump related. I think there is a weep hole on the bottom and on the top of the pump if you have a v8. Look for this in the shaft housing. Look for coolant streaks. Leaks also occur around the thermostat housing but it wouldn't make noise. Another thought is your heater valve hoses. There are exceptions to my thinking, my Camaro had a very slow leak out of the two rear freeze plugs. One behind the starter and the other by the oil filter. These are not hard to change on my 350, took about an hour. I'm still leaning towards pump if you think a noise is associated with it. Get a long piece of hose or a screwdriver and with your engine running hold one end to you ear and the other to where ever you think the noise is coming from, stethoscope. Try to pin point the noise and just look for coolant traces. Check this stuff first and then post back. Gaskets fail but let's keep it simple first.

 

Very common for the water pump to leak; but since it'e inside the pulley, all the coolant gets dispersed to where you don't notice it. If the WP is noisy AT ALL, replace it and see if the leak quits.

 

I had a real slow leak where I had to add a pint of coolant once a month..

It was leaking from the intake manifold on the front passenger side. The seam where the intake manifold and head met was green from the leaking Prestone. I could see it when I looked between the Valve cover and intake manifold.

It wasn't leaking into my oil, so I thought I'd let it ride because the leak was so slow... But one day I parked the car and saw coolant pouring out on the ground. The gasket failed completely and coolant was spurting out. (Fortunately everything was leaking outside the engine and no coolant got in the oil).

I had to pull the intake and replace the gasket.. It was a PITA...

 

I'm one board with checking the water pump. A whining noise and slow, hard to find leak both point to it.

 

go to your local advance , auot zone , etc. . most will pressure test system free . while its under pressure and the engine not running look everywhere .
[ bring a good flash light ] i found a leaking htr. valve this way that had me climbing the wall . hope you find the leak .

 

I just found a leak in my thermostat housing. The foreward mounting flange where it's cast to the thermostat housing had a small crack. Very difficult to see.
GW