What does tension sound like? Tension, in the case, meaning the feeling that if you don't complete your task in time, you will fail or be attacked. You have :05 to sell it.
(This is one of those questions that has no context. But that's ok, because the assignment doesn't really have a specific context, either.)
UPDATE: No ticking clocksNo ticking clocks! But you may incorporate other sounds that could evoke elements of time… UPDATE
UPDATE: No heartbeatsNo heartbeats! But you may incorporate other sounds that could evoke awareness of one's one's own self…