Hi there, I just installed Win7 on my HP mini last night with the same problem. My mic doens't work and I get an occasional speaker pop for no reason. The only other thing I notice is that the fan seems to run in a tad louder than with XP, but maybe I'm making that up. Please let me know if you have made any progress on this stuff.
I had the same problem with Win7 on my HP Mini as well. I was able to solve the issue by installing HP's Vista audio drivers. I found this solution on another HP Mini forum: http://myhpmini.com/forum/viewtopic.php?f=7&t=342 . This solution also appears to resolve the poor audio quality issue (that was driving me crazy, when I was still running the OEM Win XP).After installing the drivers provided by HP (http://h10025.www1.hp.com/ewfrf/wc/softwareDownloadIndex?softwareitem=ob-66804-1&lc=en&dlc=en&cc=us&os=2093&product=3744198), my on-board microphone started working again.