clicking noise, reverse only, wipers OK (steam, 4-8-2)

[BayDraw]

My long dormant light mountain 4-8-2 makes an irregular clicking noise (the noise is near constant but not in a regular pattern). The wipers on the drivers all look fine and touching where they should, the drivers don't appear to be out of quarter or misaligned, and valve gear mostly looks OK. (The one point at which valve gear parts might be touching slightly is not in sync with the clicking noises).  Also, I've very sparingly oiled the valve gear and driver bearings (Labelle #108), and run it (on the bench) at slow to moderate speeds in forward and reverse for about an hour (in the hope of working out any "set" in the drive belt). Running it only made the clicking worse.

UPDATE: I installed an NCE decoder. As a result, the clicking noise now is more like somewhat irregular growling. It still only occurs in reverse; forward is fairly quiet (though not as quiet as current production like the dcc/sound 2-8-2).

Thanks for any suggestions as to what else the problem might be. Also, does anyone have any experience to report about sending this kind of problem in to Bachmann for repair (at the cost of $45 plus shipping)? Or is this something one just lives with?

[RAM]

I would say remove the shell so you can see inside.

[Irbricksceo]

I had the same Issue with my decapod, and I found that one of the rods in the valve gear was bowed inward, causing it to "clip" into the side rod in reverse (going fowards the rod tended to be held slightly farther out and thus it didn't happen). You might want to check that no rods are hitting each other.