Very. They run on rubber tires on the rail instead of metal to metal. The electric motors are very quiet as well even when they’re accelerating but especially when they’re cruising.
I hate to bring up the Disney monorail, but if you’ve ever been around one of those, that’s about the upper limit for the noise level. Another example would be the Dallas or Houston light rail systems - only they’re louder because they are metal to metal drive. Powertrain noise (the hum) should be about the same.
Rubber, pneumatic tires are going to reduce the fuel efficiency over steel on steel.