Why do some locomotives have/use bells, but some don't?

Yesterday while in Metro-North territory, I noticed the following:

(1) Amtrak locomotives use bells when passing through the station where I was, even when they don't stop.

(2) Metro-North EMUs don't use bells, even when stopping at the station where I was.

Are bells (or whatever the clanging sound device is) required by some FRA regulation or the like? If so, only at certain times and on certain pieces of equipment? I assume that Metro-North EMUs aren't generally used in territory where there are grade crossings; maybe that's the reason why they don't have them (if they don't)?

Just curious. Thanks.

Bells on Locomotives are a rules requirement, EMU's do not have bells.

Thanks! Out of curiosity--why? Wouldn't locomotives and EMUs both have the same ability to run over someone, if the point is to alert people about approaching trains?

Bells are not even required by FRA rules, only by company rules.