noise on 2nd and subsequent tracks


I am having a problem when I record muliple tracks. The first track is always perfect, no noise, no buzz, no problems. Whenever I add subsequent tracks everything is fine for the first 25 to 30 seconds then I start to hear noise on playback. I reloaded Audacity 1.2.6 and the ammount of noise is less, but not acceptable. This happens using microphones, guitars, whatever. I am using a dell Inspiron 1501 which does not seem to be the best laptop in general, but when I first got it running under Vista I could make decent multi track recordings. The problem was Vista was so unstable that I went to LINUX (will not run on a dell Inspiron 1501, thanks Bill and the folks at MS) so I had it reloaded with XP. Now I can`t get multitrack Audacity recordings as mentioned above. Could it be the sound card? Does anyone have any idea why this should be happening? Thanks for any help.

Try setting the Audio I/O preferences to record in mono, and on the Quality tab set it to 44100Hz 16 bit.
Disconnect from the internet, and shut down all programs including your anti-virus program. How many tracks can you record?