My old Sonata (MY-y2k, 2.4l4cyl) would go through similar issues to what the OP stated using aftermarket belts. took it to my local indie when they started squealing. replaced with something aftermarket/ a "lifetime warranty". week later, chirp, chirp,chirp. take it back to him. tightens it down.
couple months later. squeal is back. replaces again(for free this time)with the same re tighten after a week or so.
couple more moths down the road, same thing again.
this time he ordered the OE Hyundai belts from the dealer.(still on his dime)
never had another belt issue for the remaining time i owned the car (~2yrs)