To go back to Ace's discussion re the Lionel 246, and Jumijo's comment re dc., my 246 runs much quieter on dc.
Another poster said his sounds like a gravel crusher, and my is the same on ac. I'm new to this forum, and I have the contributors to thank for rescuing me from my recently purchased (used) locomotive noise! Before discovering this forum, I didn't know these motors run on ac or dc. My Lionel General, a gift over fifty years ago, also runs better on dc. Thanks again!
Jon