Okay, taking care of it today is very wise. Even if money is a struggle, try to remember that the cost of a gallon of coolant is far cheaper than the cost of a new engine.
As ok4450 mentioned, the noise that you described is much more likely to be coming from a bad wheel bearing, or even from a differential that is going dry. The dipstick for the gear oil can be hard to see, so be sure to look very far down on the passenger side, using a flashlight. The handle should be yellow, but it is possible that grime has discolored it and made it hard to detect.