If you run the engine in reverse, does it dropout at the exact same location?
If you face the engine the other direction, does it dropout at the exact same location?
I realize at 14V the engine is moving along and may be hard to pin-point the problem location down to a track-tie...but above experiments might help isolate if the drop-out occurs when one or the other pickup roller passes some particular point...or maybe when the driver wheels with the traction tires passes some particular point...or may uncover some other unusual behavior.
My guess is some mechanical mis-alignment in the electrical pickups in that specific engine..in the rollers or the wheels or both. And that specific track section has some slight anomaly that forms the perfect storm relative to just that engine.
I believe it's safe to assume the whistle keeps the sounds running because the transformer puts out a modified track voltage when the Whistle button is held down.
If you release the Z-4000 Whistle button just before you reach the problem area...and the whistle is playing its several-second "tail" sound as it fades off (assuming your engine's whistle has that) I'll bet the whistle sound cuts out.
