PETER NOONE of Herman's Hermits (who will be visiting Milwaukee Sunday, July 31) displays a philosophical bent on his latest single, "This Door Swings Both Ways" (MGM). To the customary frolicking Hermit tempo, Pete, alias Herman declares that life is "bttersweet," and that one must accept the good with the bad. "This Door Swings Both Ways, lets in joy and pain. In comes the morning sun and then the evening rain." asserts his hearty tenor-trimmed with a crisp Manchester accent. He is aided by the staccato harmony of his Hermits, while a piano and pizzicato guitar fill the wordless intervals.