Something that sounds good but has no true meaning

It is a mistake to assume that every concept imaginable can be expressed by a unique word. English is lexically rich, but not that rich. Sometimes you must resort to more than one word, a phrase, a clause, a sentence, or even a book.

There are nouns that mean close to what you seem to want to convey. "Nonsense" is a common noun to express lack of logical or factual substance, but "nonsense" by itself does not imply that it is pleasant or plausible. A "commonplace" and a "platitude" mean that a thought is both commonly held and expressed in a formulaic way, but that does not make the thought nonsense. "Vacuous" is an adjective that means lacking logical and factual substance, but it does not imply "pleasant" or "plausible." This is where a thesaurus comes in handy.

Of course, once you let yourself combine nouns and adjectives, you have a wealth of possibilities: "sweet nothings," "meaningless pap," "vacuous platitudes," and "platitudinous nonsense" are examples. And you can concatenate adjectives: "vacuous but plausible platitudes" expresses the sense you seem to want with a euphonious consonance.

EDIT: User Nate has suggested that "specious" is an adjective to consider.