Banana flavors come from any of several different esters produced by yeast, isoamyl acetate being the main one (as well as the main cause of banana in German hefewiezen). This ester is produced by many yeast strains, not just hefeweizen strains, but usually at levels that are not tastable. I've never tasted banana outside of the hefeweizen style, and certainly never in SNPA.
What I've definitely tasted in my and others' IPAs is that when they get older, the fruity hop character transforms into a pineapple-like flavor. Tastes like old Dole pineapple juice in those little cans. Perhaps this is what you're tasting?
Everyone's taste buds are different, it could be that you taste banana when the rest of us would taste, say, mango or pineapple.