Uh, it's pretty hard to almost impossible to actually bend the mainspring on a Smith & Wesson using just your hands. If you did, it means that the spring likely has a problem and should be replaced no matter what.
The spring is designed to flex without bending. If you do manage to bend it, chances are it's not just going to bend, but break.
The reason the spring came out in the first place is because the strain screw was backed out.
The rattling noise you are hearing is NOT the main spring.
It is the hammer block safety bar.
This is an L-shaped piece at the upper end that has a hook eye at the lower. The eye fits over a stud on the rebound slide, and the L-shape is, when the trigger is forward, pushed up between the hammer and the frame, making it impossible for a crushing blow to either break or bend the hammer to the point where it will fire a cartridge.
The hammer block safety bar is free-floating in a groove in the side plate and is SUPPOSED to rattle. If it doesn't rattle, it could mean simply that the gun is dirty and needs to be cleaned, it is held in place by grease or oil after a cleaning and lubrication, it is bent and binding in its cut, or that it has been removed.
Condition 1 and 2 are not bad. Condition 3 is worse, as it could affect the trigger pull, condition 4 is the worst, as it means that a safety mechanism that is integral to the gun's design (and which, unlike many other safety mechanisms, normally doesn't affect the trigger pull smoothness or weight at all) has been defeated.
If you do decide to remove the sideplate, do NOT, under any circumstance, PRY the sideplate out of position! This can warp it, and at very least normally results in cosmetic damage to the frame and sideplate where they mate.
The proper method for removing the side plate is to remove all screws, and then using a wooden hammer handle, strike squarely across the side of the GRIP frame.
Keep your thumb lightly over the sideplate to prevent it flying off and landing on the floor.
This will also free the hammer block safety bar.
I recommend, however, that you do NOT remove the sideplate until you get a look at an "exploded view" of the gun that shows the different parts in proper relation when the sideplate is off.
This makes reassembling things a LOT easier.