If I'm not mistaken, you can get an electronic e-unit from Lionel for about 15 dollars. I think some of the other electronic places have them also.
Any mechanical e-unit makes a noise, sometimes a weak buss, sometimes a loud shatter. It's all in the plunger which is attracted by the coil. If it has to much space it makes a loud sound, if it's dirty and doesn't go all the way up, it also makes a loud sound. In terms of electricity, if you work with 50Hz in europe, e-units also produce more noise.
You could clean the unit, don't use oil or grease on the plunger. May be it has dust in it, or a bit of corrosion preventing the plunger to move freely. If the plunger goes easy and all the way up, the only sound it makes is a weak buzz. The louder sounds indicate that the plunger is blocked or trapped before it is in place.