  We experimentally investigate the rheology and stress fluctuations of
granules densely suspended in silicone oil. We find that both thickening
strength and stress fluctuations significantly weaken with oil viscosity
$\eta_0$. Comparison of our rheological results to the Wyart-Cates model for
describing different dynamic jamming states suggests a transition from
frictional contacts to lubrication interactions as $\eta_0$ increases. To
clarify the contribution from viscous interactions to the rheology, we
systematically measure stress fluctuations in various flow states. Reduction of
stress fluctuations with $\eta_0$ indicates that a strong lubrication layer
greatly inhibits force correlations among particles. Measuring stress
fluctuations in the strong shear thickening regime, we observe a crossover from
asymmetric Gamma to symmetric Gaussian distributions and associated with it a
decrease of lateral (radial) correlation length $\xi$ with increasing shear
rate.
