Recording lags behind and speed/pitch changes

[Martyn]

New here and thought I'd already posted this but here goes again:
I play guitar through a Yamaha Magicstomp into my computer (XP) sound card (Audigy 2) and recordings of this and a backing track works fine. I did find there was a very slight latency issue but only occasionally and barely noticeable if you weren't listening for it, but there was also a very faint background hum/hiss or crackle that most wouldn't hear until the track fades out at the end. I tweaked various settings and am still working on that, as I imagine it's just a case of adjusting levels on the various components in the chain.

A colleague suggested a USB Audio Interface would probably eliminate all of these issues so I bought an Alesis i02 two channel unit that had been highly recommended. Installed the latest drivers from their site, did the necessary allocation of sound sources on the computer, changing from the Audigy to the Alesis and it plays fine when I'm not trying to record. The sound is certainly cleaner and purer and there's no latency or any other issue. However when I try to record using the Audacity software, my guitar recording trails behind the backing track by a second or two (the vertical line definitely has a gap between it and the recorded sound I'm making) and varies in pitch, going up by a semi or full tone and, more bizarrely, speeds itself up and down too.

I tried everything I could think of but ended up uninstalling the Alesis and its drivers, whereupon the system reverted back to the Audigy 2 as its record and playback device and everything worked fine again when I tried a fresh recording. I rebooted the machine, just to be sure things reverted correctly and recognised the changes. Now logic suggests the Alesis was the new kid on the block and that caused the problem but my question is whether the Alesis doesn't function happily with Audacity or vice versa. Since I could play through the system using the Alesis and all was well, it would suggest that device is working properly but for some reason something's not right when I mix that with Audacity. Any ideas or suggestions please?

[Martyn]

Has nobody any suggestions?