Welcome to the forum! Glad to hear that you are getting interested in Lionel trains.
First, what is the number of your locomotive? This helps us research it to get you answers.
It sounds like the buzzing you hear is from what is called an 'E' unit which is an electro-mechanical switch that is used to reverse the direction of the locomotive. The buzzing is normal, and some say adds to the charm of these older locomotives.
There is a lever sticking out of the loco, either on the top, or the bottom, depending on your exact loco. This lever is from the 'E' unit, and if you get the loco going forward, pushing the lever will lock it into that direction. If the 'E' unit is not locked, the loco will cycle in the Forward-Neutral-Reverse-Neutral sequence every time power is interrupted.
There are electronic reverse units you can purchase if you want to replace the 'E' unit with one, but you may have to do a custom installation if you are up to it.
The ZW transformer may need routine service of replacing the rollers and probably the AC cord. The circuit breaker may need replacing also.
Make sure you clean the track, roller pickups and wheels on the loco and all rolling stock with Naphtha to get rid of all dirt and gunk that will inhibit good performance.
Visiting the Strasburg Railroad museum many years ago was a highlight of my life. I remember looking at the Big Boy and imagining what it was like to see and hear one of them pulling a long train battling Sherman Hill.
Hope this helps,
Larry