Uncle Vernon made another funny noise, like a mouse being trodden on.
—Harry Potter and the Sorcerer’s Stone
Is ‘being’ a passive auxiliary verb or a progressive one?
In this particular case, there is a difference. But only because -- as usual -- the sentence has been modified by a transformation. Twice.
The noun phrase in question:
consists of an NP another funny noise, modified by a reduced nonrestrictive relative clause, which itself contains a reduced restrictive relative clause.
but both of the entirely predictable [which was] parts of these relative clauses have been deleted by Whiz-Deletion, leaving behind only whatever followed the deleted auxiliary forms of be.
That's two tensed forms of be that aren't present (but can be accounted for), plus one being that's still present, for which an account is requested.
The auxiliary chain, and Verb Prases generally, are explained in the VP study guide.