Tender whistle “rattle”

Basically, it is in dire need of a good servicing/cleaning that would encompass brushes, brush springs, commutator, a good lube, and in this case, possibly even a new WS-156 bearing. The bearing is best left for those with proper tooling and experience.

Ouch. I hadn’t even finished and got the answer. Thanks. My repairman is a month out but I won’t be trying all that.
when I get a similar sound from accessories, it’s the saMe kind of problem?

Many of Lionel's classic accessories have solenoids or vibrator motors that vibrate with the 60Hz of the AC power and isn't necessarily an indicator of trouble. Whistle motors are notorious for being overlooked and thus are almost always overdue for service to the point that the bearings have become worn beyond their service limits.

You might be hearing the motor for the whistle winding up and increasing in speed until it reaches the point that the whistle works.  A tiny bit of oil on the whistle motor shaft might be a good idea in case it is stiff and dry. Bmoran4 suggestions are spot on to restore the air whistle to its as-new condition.  To his comments I'd add cleaning and adjusting the whistle relay.  But there are some things a novice can do on their own.  Check for any cracks or openings in the whistle chamber that could affect the whistle sound.  Finally, remove the engine from the track so only the tender is on the track.  Turn up your transformer a bit to operating voltage and see if the whistle works better without sharing power with the engine. I've had some success with "limbering up" the whistle motor at the beginning of the Christmas season and then it works better after that. Sometimes it's a case of learning how to modulate the transformer whistle button/levers for the best whistle sound.

Both of my postwar steamers have this winding up/rattle sound with the air whistle.  I always thought this sound was the nature of the beast, and just part of the Lionel air whistle effect.

Dale