I would definitely pull up a corner of the carpet to see what's going on underneath. This should not be a big deal since you say this is under the bed. You didn't specify the period of time that you think the leak existed. If it was a "one time thing" then I would not be too concerned, but it has been on going for awhile, you may have some issues with the wood subfloor. Best to know sooner rather than later!
Also, make sure you resolve the leak problem! No point in fixing the carpet and/or floor if the leak is still there.