Resolved by Dunning-Kruger!
I have one of these HD 1501MG servos. I'm having problems with it fluttering towards the end of travel. I would guess it's the pot inside with a bad spot or some grease on the wiper. I took the servo apart but it a sealed unit. Also I'm only getting about 60 degrees of travel. Has anyone seen any of this behavior using this servo? I thought it may just be this unit but I found a couple reviews with people having the same problems. I also found a video by our own josh demonstrating this servo and he had the same issue. Maybe it just effects a few servos and not all? Any ideas?
This would be a perfect servo for me as I need a standard size servo no bigger then this one and it needs to be analog with as much torque as I can find. The torqueier standard size analog servos seem to be going away in loo of digital. I'm using a Hitec HS-545MG now and it's just barely doing the job. It's OK with springs added but I really don't want to use them. 
Here's Josh's Vid. You can see the flutter at about 2:50 point.
Do you have another servo to test? Fluttering usually means a bad pot... I google them and found limited stats for this servo... One web site stated that it's pulse range is 500us to 2100us ... Which makes me wonder why it isn't all the way to 2500us? Or is 2100 us a typo or just normal for 180 deg servos...? I assume the pot has be extracted and relocated on the output shaft?
@Dave.
I don't know if this will help you Dave. Nobody is giving much away in the specs department about these servos, but i managed to find a little info and put a few links up for you that you may find helpful. The first one says that it has a +/- 60 degree turn. The second is the insides of the servo in question, and the third is a reviews section where people were asking about increasing it's travel, no answers but it looks like it has a limited movement less than 180. Have a look and see what you can make of it.
1501 servo range and click "Specification".
Stripping a 1501 servo
Turnigy 1501 servo discussion
Thanks guys for the input.
@Richard, I should have mentioned that the pot I have is still installed in the servo and not relocated. I'm not sure about the setup that Josh is showing in his video above but ServoCity's gear boxes come with or without an external pot. I was guessing that the one he shows did not have the servos internal pot removed. Maybe I'll get lucky and he will chime in here. However I do think the problem with the flutter is the pot. I don't have another servo of this kind to test. However other types of servos do work just fine in this location.
@Steve, Following your kindly provided links (Thanks by the way) I found a datasheet link to the Power HD company for this servo (not the Spec tab).
Power HD HD-1501MG Datasheet
It shows this servo's operating range at 180 degrees ± 10.
BTW, your last link is to a different servo I think. Thanks anyway.
@Dave... I think the pot has to be relocate to the final output shaft (because of the gear change ). The servo still turns 180 but the large wheel only turns a fraction of that... Putting the pot on the large wheel will give you the 180 drgrees as normal...
If you're only getting about 60 degs then you must have a 3 to 1 gear ratio on the large external gear....
No problem Dave. Yeah I wasn't sure about the servo in the last link, but added it anyway as it had the same model number. I just had a look at the data sheet. I'm just curious why the specification info stated the servo is +/-60 degree, and as you said the data sheet says 180? Still, 60 degree, 180 degree, I wouldn't expect or like a servo to shudder like that when it reached maximum travel. confused
@Steve.... the reference in the specifications you posted to 60deg is for speed... 0.14 seconds to reach 60degs at 4.8V.... It doesn't mentioned whether or not it is a 180deg servo but we should assume it is otherwise it would have been mentioned in the specs...
Edit Dave's PDF confirms it is a 180deg servo.... The pot has to be relocated to the large output shaft if you want to get 180 deg of rotation with the new gearing...
@Richard, I'm not useing the gear box like Josh shows, just the stright servo, no gearbox. Sorry for any confusion.
I just wanted to show that video to illustrate that I'm having the same issue. Also the link I posted leads to a data sheet saying that it travels 180. In reality it will only physically only turn 90 degrees but when commanded by ARC to move from 1 to 180 it will only move about 60 % of what it's capable of moving. Just like what Josh stats in his video above. Yes I have the servo control configured from 1 to 180.
@Richard.
Okay, gotcha. To me it looked like it was saying it could travel 60 degrees in one direction or the other from centre position. But a picture I found looks like it should rotate 180 full travel. Blame it on lack of coffee.