I'd say 4E or 4F among the options you have on 773 if you want to stay away from the noise. (Proviso: no potential passenger noise has been accounted for, except for the loo noise.)

There are double-curtains behind Row 4, i.e. there are curtains, then a loo behind 4A/4K, then another set of curtains, and then the CW galley. It's not very likely that you'd be bothered too much by the light because of it (the area between those two sets of curtains is quite dark, and double set of curtains also dampens down the noise from the CW galley).

You are less likely to be disturbed the loo noise directly behind by sitting in 4E/F (whereas you might hear it in 4A/K), and also less likely to be disturbed by the light/noise from the First galley that you may get in row 1.