Why not simply record a real trolley using a digital recorder (which start at around $25) and then use that device?  I suppose you could get fancy and copy the recorded sound to a computer or PCB, but I'm thinking the handheld might get you up and running the quickest and you could always choose to change / augment your list of bells.

I'm not sure what's available in your area, but around Chicago there is the Illinois Railway Museum, the Fox River Trolley Museum, and the East Troy Electric Railroad.  All have working trolleys.  While I haven't done any research, I cannot believe these are the only museums with working trolleys.

I agree with your decision not to use a real bell.  Not that it would be too loud, but rather capturing their inherent muffling would, - IMHO, be a chore (all the ones I have heard kind of end like they get wrapped in a towel rather than continue to ring).

Which MRC handheld are you using?  If it is the Prodigy Express then there's not much you can do in the way of troubleshooting.  If you have the Prodigy Advanced 2 *squared* (PA2) then it has the capability to set up a programming track.  The programming track will let you read the various CV values.  Check out this link to MRC's website for some additional documentation on the PA2 (there's links to PDF's at the bottom of the page):  http://www.modelrec.com/search/product-view.asp?ID=7735

Personally I would look at the starting voltage.  It could simply be that the way the motors were wound that they need more (or less) voltage to get them turning.  My Spectrum 2-8-0 needed to have this setting adjusted in order to get it to start at step #1.  As GN.2 pointed out, you may not be able to have this particular locomotive running using 128 speed steps (or even 28).  There should be a Speed / Spd Step button on the bottom left of the handheld.  Pressing it shows the current speed step setting.  If you press it again it will go to the next setting (cycling through 14 / 28 / 128).  Press the Enter key when the one you want is displayed (and don't forget to unplug the handheld so it saves your setting for that locomotive).  Each locomotive can have its own speed step setting, so you may need to repeat this process (as well as setting it again if you delete the locomotive's address from the handheld).

Another thing to check would be to make sure there's nothing binding on the locomotive.  While these units are belt-driven, they are also designed so the belts do not slip.  Any resistance could prevent the motor from turning at slow speeds.  You mentioned similar behavior with other locomotives - just because they are diesels / direct drive doesn't mean they cannot be binding.  Mass production does not guarantee consistent quality / performance.

If the performance is that bad you may want to contact Bachmann's service department to see if they would be willing to swap out the motor (as it doesn't sound like a decoder issue).  The lifetime guarantee is one of the wonderful things with the Spectrum units (although to be honest I've never needed to use it).

You may also want to check out the MRC-DCC forum on Yahoo! Groups.  There are some folks there that have quite a bit of knowledge when it comes to decoders (of any kind) and how to get them to work well with the MRC controllers.