Yep, but now that we know that, we're sure that it isn't because of some foreign element in the system, so we start investigating other possible causes, like the configuration of the circuit.

[Geordi starts looking over the omnicorder again, nodding at the readings. Exactly the kind of things he's expecting to find. As he examines them, he goes back to the topic of cloaking technology.]

Starfleet doesn't have that technology, either, but we've run into some who do, like the Romulans.