Most of the common wireless weather stations use some form of Manchester coding, http://www.atmel.com/images/doc9164.pdf
to transmit the data, as this provides a more reliable form of transmission.
Usually there is a framing sequence of some kind consisting of alternating 1 and 0 to allow the AGC in the receiver to stabilise.
The best way to figure out what is being sent is to get one of the sensors, like a temperature sensor and capture what it sends .
You will have to pull it apart and sample the data on the data pin of the Transmitter Module.
The benefit of looking at the transmitted data is that it gets rid of all the other signals and interferance that confuses what you are seeing.
You are going to need something better than a sound card though to do this, some kind of CRO at a minimum to capture the entire data sequence, as you have to figure out if any kind of CRC is used or not.
The CRC is sent at the end of the transmission.