need help with strange motor sounds

Hi. I've been troubleshooting this problem off and on for weeks now. And it's finally got me stumped.
I've got a Sanguinololu 1.3a board with ATmega 1284p chip and sprinter firmware.
Running with Pololus drivers and Nema 17 stepper motors.
Running a PC power supply with 500 watts.
All of my X, Y and Extruder motors act like the videos I posted for jitter1 and jitter2.
Only the Z motor runs good, video is the smooth one.
I can swap motor drivers, and still only the Z motor runs smooth.
I can swap motors around, and still only the motor hooked to Z axis runs smooth.
I've tried marlin and sprinter, both run the same way.
I've adjusted the trim on all drivers up and down, same behavior, except that when I turn it down nearly all the way it'll stop moving or make lessor erratic sounds.
At one point during my testing, all my motors ran smooth for a just a few seconds while I was sending commands through printerface. And then without any other changes, it went back to acting jittery again.
And this morning when I first turned everything on to try and take these videos, the extruder motor ran good for just a few seconds, and then while it was still running an initial test, I could hear it slowly run towards erratic, jittery movement again. After that, it always seem to run bad for my video taking.
I also tried including a stepper delay in my code last night after reading that it helped one other user on here. That didn't seem to help my problem.

At this point all I can think of is that I've got a problem with my circuit board itself or possibly the same off settings in firmware that could be in both marlin and sprinter?
Any suggestions?
I'm not sure where to go from here.
Thank you in advance for any advice you can give that might help!
Chris

can you list your configuration.h and pins.h file. also have you tried alternating wires on A? make -A ->A and then -A->A. does this fix the issue?

Here are my config files you asked about.
The odd thing about my shaking motors is that:
1. I can move any of the wire connectors onto the Z: connector on my board and they'll start working smoothly, no problems.
2. a couple of times, I've seen the motors initially turn smoothly and then all of a sudden go to studdering/shaking while in the middle of a printerface command.
Do you think my power supply could be causing this? I would think if its the power supply it would make all motors (including Z) act up like this.
Thanks for any advice you can give!
Chris

I tried swapping the A wires, my two wires connected in the middle of my pololus,
hooked it to the extruder driver and clicked extrude 1mm. I heard a quick click out of the motor, with no movement.
And after that I couldn't get any more movement from it with additional extrude commands until I reset all of the power, usb connections, etc.
Then I switched the A wires back and then was able to get some erratic movement from it.
So, i shut power off, moved the motor to the Z axis, and turned it back on and clicked the 1 movement in pronterface.
smooth movement once again from the same motor.

Edited 1 time(s). Last edit at 11/07/2013 08:00AM by cbearden.

Good news! I feel like I'm a lot closer to solving this.
I was able to get my X,Y axis motors to turn decent by adjusting my axis_step_per_unit values in the configuration.h file.
I changed X and Y from 700 to 84, and that seemed to help quite a bit.
Then I moved onto my E value. I tried all sorts of values in pronterface with
M92 E700
M92 E70
M92 E2000
M92 E1500
all values either made a very loud sound and no movement at all,
or a lesser sounds with very limited movement.
So, at this point, I'm trying to figure out what to set my E value at, and also what speed mm/min to use in pronterface to test with.
also tried multiple speed settings with limited results.
Using the typical calculations from one of the online calibration guides,
// Classic Wade with a 39:11 gear ratio (200 * 16) * (39 / 11) / (7 * 3.14159) = 515.91048.
I tried setting it with
M92 E516 as an example, but I still got loud or limited results.
And that's about where I'm at.
Any suggestions on what I should be using for the E value?

Also, I'm using a wade extruder, so I'm thinking this value of 515.91048 might be correct. But I'm just not sure what value I need to use in the pronterface GUI for the speed mm/min value?