cooling system troubles

hello, just recently i started leaking coolant, a week or 2 went by before i finally figured out where it was leaking out of, on the bottom of the coolant resevoir there is a sensor with a connector with 2 wires, coolant was dripping out of that opening, it only does it sometimes though, i unplugged the sensor to inspect the connector, it looks fine, so now im wondering, if i pull that resevoir out, can i unscrew that sensor, put some teflon tape on the threads and be fine again, or will i have to replace the whole resevoir??

on to the second part of the question....

when it gets REALLY low on coolant the resevoir will starting making this weird noise, at first it sounded like a small animal was trapped in it beating on the walls trying to get out, but im assuming its really just a suction noise, the radiator trying to suck coolant and getting nothing but air, is that the case?

the first time it made that noise i didnt do anything about it cuz i was busy, i was in heavy traffic, and my car wasnt overheating, so i didnt worry, the second time i decided to pull over right away and refill the resevoir, so i do that, i leave the engine running, pop the hood, its still making the noise, i remove the resevoir cap and the noise instantly stops, about 3 seconds later the resevoir instantly refills on its own and starts overflowing, i shut the engine off immediately then the over flowing stops, however the coolant level in the resevoir did not go back down, i put the cap back on without being able to refill it, drove it back home and it was fine the entire way, when i went to leave my house next the resevoir was empty so i refilled it before even starting my car, im basically wondering what exactly happened there with the overflowing?? what caused that??

It is a sealed system- (has the radiator cap on the reservoir) these can be tricky to get them full of coolant- as you have found out- it is best toi filll cold. The sound that quit when you removed the cap is the system trying to suck in or expel air through a leak location- most likely- your cracked or leaking coolant sensor connection- this whole situation may be easily fixed by sealing that leak- or by replacing the reservoir- (salvage yard would be where I'd go) - If that doesn't work then you need to know if the radiator is not plugged, that the fan comes on etc- but start with making sure it always has enough coolant in it- by fixing that leak.