A lot of spring noise is caused by the cut end of the wire of the spring. This sharp edge digs into the washer it's pressing against, and that makes it prone to move in sudden jumps, rather than a smooth sliding action. The best solution is to use a grinding tool to carefully round off the end of the spring wire, so there's no sharp edges. This can be done by hand, but it's a lot easier with a small power tool, such as those made by Dremel, RotaCraft, Expo, Proxxon etc etc.
It's possibly slightly better to try and polish the rounded-off end, but if you use a fairly fine abrasive for the main work, it shouldn't be needed.
Likewise, I don't think it's necessary to try and get the end of the spring flat, like on a vehicle suspension spring .... that's more to do with keeping the spring straight during compression/extension cycles, prolonging service life.