Noticed this while looking at car from the rear

Correct. Any angularity indicates some of the all-too-common rear suspension collapse, which also affects camber and toe in. You can replace the rear cross-brace above the trans with one having an adjustment turnbuckle. I suggest the cheaper steel unit that is longer and jams back into the welded pocket of each rear inner fender, rather than the shorter alloy type where all the load is carried by a bolt thru tabs on the pockets. Don't try to adjust everything out this way, or you'll distort the rear panels enough to crack your paint. Then, realign the rear wheels.