I'm not a big fan of 2D NOESY for small molecules in the extreme narrowing region. I find that the gradient selective pulse 1D NOESY experiments (available from the "Selective" panel in Topspin) are much better and can detect NOEs down to a small fraction of 1%. When you get to slightly larger molecules, at the cross-over between extreme narrowing and spin diffusion, then the corresponding 1D ROESY experiments (especially the modification by Julien Furrer J. Nat. Prod. 72, 1437, 2009). work very well.

If you really need the 2D experiment, then check for things that tend to cause T1 noise: vibration, room temperature stability, proper PID parameters in the VT unit, good sample, proper lock parameters, etc. I'm suspicious of processing algorithms, including symmetrisation, for reducing T1 noise.

Also, I think your mixing time might be a bit long. It's always a competition between NOE build-up and relaxation. I find that about 500 ms. tends to be a bit better for most things.

100 mg is probably a bit to high for concentration at this MW (10 to 20 mg would be fine), and it helps to degas your sample to ensure maximum NOE by reducing relaxation caused by dissolved oxygen.