ES44AC Front Truck Clicking Noise

See if there is a chunk of Styrofoam or anything else in the gears.

You may have to use a dental pick or something similar to clean the teeth. By now, it will be smashed in there and maybe darkened from grease.

Is it consistent with wheel rotation speed?

I would remove the front truck (turn, twist and disconnect) and then power it up through the rear truck suspending it off the track.  Now run it and see if you hear the clicking.  If you hear it then something is impacting the flywheel of the front motor like the antenna or cab lighting shroud.

If it stops, then check the Liondrive connector and make sure the motor shaft impeller is all the way at the end of the shaft.  Make sure the impeller does not spin/slip on the shaft. 

@BobbyD - Consistent with rotation speed

@RoyBoy - Ran a flashlight over the gears and checked for debris but external gears looked fine

@Steims - Testing with rear axle powered and front axles off the track did not hear the clicking when I held the engine in place (didn't ramp up very high in terms of speed steps to prevent rear motor burning out), Next steps would be to remove the motor and take a look in the shaft. Is there a safe way to do this? I see 4 screws on the bottom where it looks like the truck connects to the motor, and the motor itself (when I take the shell off), looks like it is held in with 2 screws that are shared with the bottom 4 screws. Haven't opened up a motor shaft before so trying to be careful not to damage anything in it.

Photo from inside shell:

You proved the motor and flywheel is fine.   The clicking is either in the truck or the connection between the truck and motor.  

Secure the flywheel with one hand and try and turn the impeller with your other.  If the impellers rotated on the shaft then it needs adhesive tonn BN prevent.  The impeller should be located at the end of shaft and not slid up towards motor.  

Turn the Liondrive coupling in the truck and confirm not clicking through full wheel rotation.  

Have gone through and done surgery on the motor / truck assembly, results:

• Truck disconnected from impeller shaft and was rotating freely with no noticeable noises
• Flywheel on motor rotating freely (no contact on tach sensor)
• Holding the flywheel and trying to spin the impeller, impeller did not move (hand slipped around it)
• Impeller connector was rotating freely (that was a slippery mess and probably what caused the below issue)
• All pickup rollers are off the front truck for testing

The clicking stopped but now I think I need to pull it open again because it sounds like dirt or something may have gotten too close to the impeller / connector and is making a different clicking noise now. (Didn't want to risk damage to the cable assemblies attached to the shell so left them attached and maneuvered around them, which in hindsight was probably dumb because it took a ton of coordination to get the impeller re-aligned and attached to the frame/truck together). 

Is there a safe way to disconnect those tiny little 2 pin connectors / the big 8-10 pin connector at the front so I can do a full shell removal and test shell off? The antenna metal piece is screwed to the shell as well but I can just make sure it doesn't touch any components during testing

The 2 pin and 8 pin connectors come right apart.  I usually take a small flat blade screwdriver to force in the joint and then twist to spread it open.  Then usually can pull on the connector by hand.   Please proved the model number of you BNSF loco. 

Are you sure the clicking is not the pick up roller hitting the track joints? 

@Steims Thanks I'll try that with a thin flathead and see if I can't pop the wires out and do a full chasis-only test with flywheel exposed! The model number is: 1922061 (Oil train set: 1922060 purchase the loco independent of it), I'll try and get a video of it in action tomorrow night / Sunday.

@romiller49 Both front pickup rollers have been removed to isolate the noise.

I was unable to properly get the shell lighting wires undone, so what I did instead was hang the shell off the side and carry it while it moved. Testing shell off had no audible clicking at low speed, shell back on had audible clicking, finally figured out the mystery. When going through curves the shell looks like it moves a tiny bit (or the motor does), and it brushes against the side of the shell at higher speed, I noticed some paint on the flywheel after I did a shell-on high speed run. I pulled the shell up a bit and ran it on the circuit about 100 times, when it fell down a bit there was the audible clicking / grinding noise which confirmed indeed it was the flywheel all along causing it. The shell itself is a very tight fit on the sides (the legacy board has less than 1mm of wiggle room total on both sides to fit the shell on, so I'm wondering if I can sand down the inside a bit to resolve the scraping of the flywheel occurring.

That or take some material off the flywheel.

Before that, make sure the motor is mounted ok and fasteners are tight. It may be loose in the saddle.

I would sand the shell a bit if that is the rub.

I had some noise on a Lionel ac6000 and  found that the shroud on the front motor would make contact with the fly wheel.   When assembling the engine i had to make sure that there was no contact between them.

Marty