something is up
Something isn't right; something unexpected, undesired, or out of the ordinary is happening. Something's up with the computer—I think it may have a virus. Hold on, something is up—it shouldn't be so quiet in here.
something is up
something unusual or undesirable is afoot or happening. informal 1994 Marianne Williamson Illuminata It feels as though something is up, as though something significant and big is about to happen.