Noticed when pushing my quad around with it shutoff I can hear what sounds like a crack, crack crack sound coming from I think the rear axle where it passes through the swingarm. I don't think it's the sprocket or chain. Is this a sign of impending axle bearing failure?

It isn't rythmic & it comes & goes, but still pushes easy.

Any advice?

 

Good time to learn how to change the axle bearings. If not change them at least check them. Sounds like the bearings are starting to pile up, by the time mine made that sound it was too late, but we can't be certain unless we hear the sound in person. Try having someone life the rear of the quad off the ground and forcefully ram the alxe around via grabbing the tire. If you have play, then it's the bearings. I suggest doing it yourself, it's not that hard, and but the match bearings...(not the OEM ones), they will be like 1/3 the price. Do a search and you can get the cross reference numbers.
Hope this helped. Just ask if you have any further questions.