Tranny problems (5spd), need help ASAP!!!

Well, recently, when I am at a dead stop and try to engage in the clutch in 1st gear, it has some weird noise (kind of like the sound when you first learn to drive a 5spd and shake the car - the gear just hit each other...). This will happen only when I try to engage the clutch from a dead stop in 1st. By the way, I have been driving 5spd for years, so I am pretty sure it is not b/c of my skill.

The car has about 30k miles and I change oil every 3k miles with brand names and filter. It is kind of strange because this will only happen in 1st and 2nd sometimes(but it is not as noticiable as in 1st, although you need to pay a little bit attention to notice it in 1st.) If I rev the engine past 2500rpm, I would not hear that sound(but I am not sure if it is because that the sound of the engine is louder or not.)

I have never have this sound before and need everyone's input on this. I will have a long road trip in 2 days and definitely want to have it fixed before (or someone can tell me what it is and is not very serious.)

I appreciate any valuable information on this!