It's more like a clangy sounding rattle that comes and goes. Not so much as a transformer buzz.

My furnace buzzes sometimes when it's running and I had a guy look at it but he said the part was obsolete and blah, blah, blah. (Buy new furnace.) Not an option right now. I was wondering if this is from a limit switch and if I can replace the part myself? The thing works just fine, otherwise. It's...