pH Difference Our Taste Buds Can Recognise Water at $50~^\circ\mathrm{C}$ has a $\mathrm{pH}$ of $6.63$, while the pH of water at $0~^\circ\mathrm{C}$ is $7.47$.

The temperatures are comparable to a chilled, iced drink (at $0~^\circ\mathrm{C}$) and a hot drink (at $50~^\circ\mathrm{C}$). Would these differences in acidity be noticeable? Would they be noticeable if the drink was more acidic, such as orange juice?
First, the pH of water changes with rising temperature because the total number of $\ce{H+}$ ions (well, solvated hydronium ions, really) increases, not because it has become more alkaline. The water is still neutral, having an equal number of hydroxyl ions as hydronium ions. Heat simply increases the ionization.

Second, it depends on the individual taster, but a sample of water at $\mathbf{20~^\circ C}$ with a $\mathrm{pH}$ of $6.63$ (perhaps acidified with citric acid) would probably taste sour in comparison with a sample of water at $\mathbf{20~^\circ C}$ with a $\mathrm{pH}$ of $7.47$ (perhaps with a bit of baking soda, $\ce{NaHCO3}$).

See Temperature Dependent[sic] of the pH of pure Water for a more detailed explanation.