sound - crescendo

I have been thinking about sound for my clips. after doing a bit of research i have found some royalty free down loads but i am keen to record sound my self.
after walking around at night filming with a flip camera i extracted the audio from that and now have a good collection of sounds of traffic that i have recorded my self. after speeding these clips up and placing them next to the footage i already have its clear i need to really layer noises and some times play real time noises with the more abstract city background noise. i have been talking with Giles and we where discussing the idea of having a basic rhythm with in the piece. i really like this idea. also in my sketch book one of the key words that i have used in the planning is CRESCENDO. i really want my video to have an overall build up of energy. to achieve this the sound is as important as the visual. so when editing the final track i will have this in mind. for now i am still sourcing sounds.