The original 4/24 kernel is compatible with CM7 stable versions, but not compatible with the current nightly builds (nightlies require ext. 4 script edit).
On your side note. I'm a big believer in always backing up your stuff and doing a wipe a complete (system, data, cache, & dalvik) wipe when changing roms completely. A little extra caution goes a long way towards saving hours of frustration. Some may disagree, and that's fine it's just my opinion.
yeah I am a big believer in doing the full wipe, have done so in the roms I have flashed before.
does the current stable (7.0.3) fix the speaker buzz whilst screen is off?