First let me say I'm a complete newbie. I like trains want to start a new hobby so I bought a small set. It's Bachmann N scale from 1974 new old stock. It came with a very small oval track. About 18" across or so. I believe it's a Santa Fe Engine. I took it out of box connected it all and started it up. It pulls the four cars it came with, but that doesn't appear to be the problem. By itself, if I let it run for about five minutes or so it will start running noticeably slower. I count "1 thousand, 2 thousand" etc. It appears to run the circle in about 5 seconds very consistently for about 5 minutes or so and then over the next couple of minutes it slows to about 7 seconds.
Also, if it's relative, In the first few minutes of running the train there was an occasional high pitched whir sound accompanied with the engine appearing to stall for just a split second. This did it a few times and then settled down and hasn't done again in since.
I can't think of what else to add. Oh, I looked forward to getting sucked into this hobby. But I do want to get this figured out before I really dive in. I bought this on Ebay and want to know if I should work on sending this back and start again or if this is something simple. Thank you to all the more experienced folks in advance.