I agree on the DuoR/RX being the most reliable.  The laser assemblies are IDENTICAL to the Turbo/PCE Duo, but the hardware on the board is "different".  When I say "different", I mean it appears to be the same technically, but the capacitors and some ICs seem to be from different vendors and of larger voltage.  I know what circuit/IC controls the CD drive speed and roughly which one affects sound, but replacing capacitors hasn't yet been fruitful in eliminating the sound problem.