Strange bending in tall print - Layer shift?  

Strange bending in tall print - Layer shift?

Hi all-

I have been trying to print a part in PETG, but I'm getting weird waviness higher up in the part. My settings seem like they're properly dialed in as everything else is printing great, however this I can't seem to work out.

It happens in the same place every time. It looks almost like a layer shift, but not exactly. I'm printing at about 40mm/s with Slic3r PE (though I've tried it in S3D as well), so I don't think it's going too fast. However, it is above a bridge, so I'm not sure. The bridge isn't spectacular, but it doesn't seem terrible either. They are, however, basically symmetrical above the bridge.

It's not the model. Other people are printing it perfectly well. The person who modeled it even uses an i3 Mk2, so I know its doable.

I can also print other small models without a problem. Most of my stuff comes out great.

I asked about this on Facebook as well, and have been trying their suggestions, but without much luck. Do you have any suggestions?

My settings:

PETG
nozzle - 247
bed - 87
.3 layer height
10% infill
4 perimeters and 4 top/bottom shells
running high power mode

I've calibrated my extruder and tuned nozzle PID, and can get beautiful prints on other objects, though I rarely print anything this tall and thin. I haven't gone to linear advance yet, but plan to try soon.

I worried that it might be belt slippage, but it seems weird that it would be the same every time. Other than this the print is great, but I just can't seem to get it worked out.

I'm also a total newbie to this, so it's possible I'm missing something stupid, but I've really put a lot into figuring this out. I really want these pieces to fit together, which they won't with that stupid bulge.

I really appreciate any help you all can offer. Thank you in advance!