If you returned it for a significant squeal, Id say you have a gripe.
If its just a little squeak tough. you could say its brake squeal, because that is just as likely its only plastic vibration, and here to stay at least a while.
I have a Lionel 0-4-0 mpc, that squealed for years on startup, but thinking on it, it stopped! My WbB BL-2 was silent.
The most common issue with other Bachmann products in general seems to be gear cracks at the axle boss/hole. They can cause squeal, and can be hard to spot. They usually offer a free set if there is a model run issue, and high supply, even if they haven't cracked yet. All bearing type areas should be checked for play. I would also try and determine if excessive thrust, or run out, is present at the motor shaft
My Bachmann experiences have varied (though no O yet).
That said, it was frustrating. But actually better, and friendlier than most customer services I've dealt with in life.
So contact "customer service" if its that bad a gripe.
(Be nice, but firm and truthful in your feelings about the case).
Parts for ordering, & rma info (the nice lady that normally answered phones)(to get yelled at constantly)(but was so nice).
Techs I've talked to. You may need to too now. But I try to leave them alone to fix things.
My Emails have been answered by many there, so I don't know who does that normally. but it is the best way to start every contact.
I get the feeling everyone there helps out when, where, and as needed.
E-mail should include a day phone number too, and then make a phone follow up if necessary.
Specific notes attached to the train so they issues aren't missed, mixed up, or skipped.