Possible that they did not torque the axle nut correctly, either overloading the bearing or having too much slop. A rythmic squeek could be from a bad wheel bearing or bent axle hub. Could also be from contact from dragging brake caliper(s) - even if you are actuating the brakes, the pads slightly drag on the rotor. As you drive and put some heat into the rotors / pads - makes them expand slightly making for the possiblity of contact more likely. Also could be from contact with the dust shield around the brakes - if they manhandled the axle in there - they could have bent it down enough to touch the rotor. There are also some dush shields that fit between the axle assembly and the hub - if those are not installed right - they could make a squeeking noise.
If you jack that corner of the car in the air and spin the wheel by hand - you should be close enough to localize the source. If it is still hard to tell - you can go so far as removing the pads, put the wheel back on and then spin it. If there are no clearance issues with the dust shield and no pad - but you get a squeeking noise - then it would most likely be the wheel bearings. Now you have to see if the install was botched (a good mechanic will be able to tell if the bearing pre-load is off.)
Assuming that your driving habits didn't change and that the noise was not present before they replaced the axle - that would lead me to believe it was a botched axle install that is causing the noise. See if the place that did it will look into the matter - no charge. If they start pulling your chain and blaming something else or blaming you (a good shop will eat the diagnostic if their workmanship was contested) - then find another place to diagnose it and fix it right. If it was me - I'd send the bill to the original shop and make them pay for it. But it depends on how much time, effort, and money you want to invest into this. But you should expect a repair like this, performed by a competent mechanic, to not get messed up.
