Tension only exists when players are aware of things, or are suspicious things exist. This means that you must allow them the idea these things exist. If the trap has caught them, then it's too late for that trap, it's drama has gone.
Conversely, you don't want players stopping the game every five seconds just to 'check for traps' when it isn't appropriate. Any time a skill check becomes rote 'just cause' you're actually wasting time and you're making the process -less- tense. It's just a chore.
So -let- the high perception character be able to see traps--it takes Thievery to figure out what the trap does, and how to circumvent it, and that's MORE of an opportunity for tension.
'You see the floor has uneven stones... the dust has falling into cracks around them, and you surmise that they must be pressure plates of some type. The bugbear overlord grins as he steps on one, and you hear a loud ticking like a giant clock. Other plates raise a bit.'
'So what does it do and how will it kill us?'
'That's an excellent question that you do not have the answers to.'
'Oh... so are they good? Are they bad?'
'Even more great questions. And you have even less answers!'
'Bugger.'