This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
The noise was probably an electrolytic capacitor exploding. Sometimes, these develop internal shorts, heat up, and blow (kind of like a sealed can of beans on a campfire). The fix is to remove the drive cover and replace the blown capacitor. (Look for a small can-like component with goo and/or shredded foil coming from it.) Circuit board markings should help identify the component. Here are some suggested replacement values: C2 (on +12V line): 220uF-500uF at 20V-50V C4 (on +5V line): 470uF-500uF at 10V-25V C5 (on -12V line): 10uF-50uF at 20V-50V If there is some difficulty identifying the blown capacitor, replace it with a 500uF unit rated at 20V-50V. Before removing the bad capacitor, note which lead is connected to the outside 'can' part and mark the circuit board where this lead is connected. This is the Negative side of the capacitor. When installing the new capacitor make sure its negative lead goes to the marked point on the circuit board. By: Wayne Stewart