United traction trolley, grinding noise

[rperego]

Any ideas on adjustments etc. to eliminate grinding noise with a united traction trolley?
While converting to DCC I didn't see anything wrong with the gears and they are well lubed.
Thanks, Bob

[Flare]

Which scale trolley are you referring to?

[rperego]

G scale.
Since my 1st post I noticed it looked like the wheel gears may have been rubbing slightly on the bottom half of the case   I dremeled the plastic a bit.  This cut down on the noise but only slightly.  The worm gear lash looks about the same on both ends so I don't think it is binding at that point.  BTW, I think this unit was either NIB or very slightly used.

Meanwhile, with more testing it appears the motor doesn't respond well to incremental DCC speed increases.  I'm running on a DCC controlled point to point track with a "middle" stop (TamValley unit).  No problems with an ART railbus or a "Clemetine", both with the same decoder (NCE D13SR).  The start up and slow down is controlled by the decoder CV 3 and 4 values.
I then ran the united traction back and both using my normal DCC base/throttle. The united traction will run fairly well if kept at the same speed, but as with the TamValley shuttle unit, it doesn't gradually pick up speed very well.

All this might not matter except for my intended use on a point to point track.  Crawling out of a "station" and then suddenly going to the desired speed just doesn't look right.  One reason for going to a DCC shuttle instead of a DC shuttle with diodes was to get the incremental start/stop as well as consistent light intensity.

Still looking for suggestions but meanwhile found an article where someone gave up on the original motor brick and converted to an Aristocraft brick that is a close fit. 

Thanks,  Bob

[rperego]

Now after further examination, finding a substitute motor truck seems like the best option.
Running the unit upside down with the lower "lid" off, the noise/vibration is coming from the worm gear/spur gear junction.  Given that use of a straight cut spur gear (as opposed to spiral or helical) is prone to noise and vibration I don't think much can easily be done to improve this.  Add to this various parts that are far from precision.
Why the trolley on the track didn't respond well to DCC speed steps is a bit of a mystery.  Running upside down it responded correctly to speed steps.  It wouldn't start until step 4 but this could be rectified with Vstart CV.

It appears folks have had success using either a USA or Aristocraft motor truck.   Interested in anyone knowing where I might find one.

Thanks, Bob