thanks for the responses, gents. as for checking the layer quality, yep, that’s set to high.
what makes me suspicious is that this was fine before my harddrive crashed and AE had to be re-installed. I keep thinking there must be something somewhere that I’m forgetting to check/click/etc.
I thought perhaps it was just a visual output problem, but I loaded an uncompressed QT onto a timeline and immediately rendered it out with all output module settings set to best. and STILL it had the aliasing.