sneaking
adj.a feeling or thought that you have quietly and that grows stronger over time. You use this when you suspect something is true but you are not completely sure yet.
adj.describes a persistent, growing, but often unverified feeling or suspicion. Typically used attributively to modify nouns like 'suspicion', 'feeling', or 'doubt'.
“I have a sneaking suspicion that she is lying to us.”
“Despite the positive reports, the manager had a sneaking feeling that the project would miss its deadline.”
“He could not shake the sneaking doubt that his success was due more to his family connections than to his own professional merit.”
Almost exclusively used attributively, appearing immediately before the noun it modifies.
In this sense, 'sneaking' is an adjective that must modify a noun; it cannot be used as a standalone verb to mean 'suspect'.
“But they aren’t secretly drinking beer or planning on sneaking out.”