The waves LIGO is looking for are very macroscopic in scale. Quantum gravity will not have much effect on them in the modern universe. Quantum gravity undoubtedly affects the shape of the early universe, and some signature of it may be imprinted on the stochastic background of gravitational waves. But it will be tricky detecting that with LIGO because in its frequency band the background from lots of distant "normal" sources (neutron stars etc) is probably louder.
The non-detection of gravitational waves so far isn't a surprise. At the current sensitivity (S5 data run), we have a fighting chance of seeing something in the next couple of years. After that there will be upgrades and it will get much better. If we find nothing in S5, that starts to say something astrophysically interesting about some neutron stars and other things, but doesn't get anyone worried about Einstein's theory not describing gravity well.
Keep on crunching,