1999 Cavalier-heater not working/after sensor replacement

A few days ago I brought my 1999 automatic cavalier into the dealership because my check engine light was on. They said it needed a new coolant sensor and harness. Had them replaced, but now after 3 days, I went to put the heat on in my car and it won't work and the car is now making some type of noise. Noise is like when you put cards on bicycle spokes. Do you think this problem is related to the recent repairs? I don't want to go back and have them tell me that I need another $500.00 worth of repairs. I really hate being "mechanically" challenged and taken advantage of over car repairs. Thanks.

The check engine light is not coming on, the check gauges light is now on. The noise started after the heater broke and is not heard if it's turned off. Air does blow out, but it is cold. This morning when I went out there is some type of fluid that has leaked out all over the driveway towards the right side of the car. I can't tell what color the fluid is, but it is "oily" to the touch.

I will get the car back to the dealer for it to be checked, but I am hesitant only because everytime we've brought the car in for repairs, something else inevitably goes wrong with it within a week of us getting back from the shop.