We note that below the predicted threshold, above which hydrodynamic interactions have significant affect on bulk properties, our measure has approximate (square) power-law scaling as expected for the variance given linear growth in amplitude, which is in turn is expected if polymer coils are independent. The approximate power-scaling occurs with a concave rounding versus the strictly linear curve predicted on a log-log plot. This round- ing (breaking of power-law scaling) suggests subtle polymer-polymer interactions even in quite dilute solutions; recent systematic and careful rheological studies have demonstrated [31] polymer-polymer interactions can exist for concentrations as low as 1% of the overlap concentration in elogational flows. The lack of true power-law scaling at low concentrations, the mild decrease in fluctua- tions above a threshold, and the correspondence of this observed threshold with the predicted threshold for hydrodynamic interactions in (hard) colloids and (soft) polymers indicate hy- drodynamic interactions are important in nominally dilute solutions and limit fluctuation growth. FIG. 6: Fluctuations at various concentrations. The fluctuations in normalized PMT voltage for HMW polymer at different concentrations and 0.2 kV. It can be seen that fluctuations increase with concentration but rapidly peak and plateau well below the overlap concentration ( ≈ 0.1 c$_{∗}$ ; c$_{∗}$ ≈ 300 here). Modeling the polymeric solution as a hard colloidal suspension predicts a transition in behavior at c ≈ 40-60 ppm (grey band) due to molecular crowding. Simulations of a similar polymer [29] find a threshold of 0.1 c$_{∗}$ (dotted line) above which hydrodynamic interactions between polymer coils significantly affects properties. The good agreement of both the colloidal model and the simulations with the observed peaking of fluctuation growth suggests hydrodynamic interactions and molecular crowding is the mechanism inhibiting fluctuations. 11