OK. Well, apparently a lot of people do have confusing audio issues with that series in particular. Have you tried these things (you probably have tried some)?

1. Run with no battery in it (just on AC)
2. Run with no AC (just on battery)
3. Updated the BIOS and/or played with device settings at the BIOS level
4. Make sure "Drive Guard" or whatever HP calls it is uninstalled
5. Creating a new user account on the laptop, and seeing if it has the same issues (this test in particular can point at very specific things, although this particular problem seems unlikely to be one of them)

Can you be more specific about the model? I wanted to look at what drivers exactly they recommend, but there are multiple dv7 models. dv7-1245dx, dv7-1000, etc.