I have a music keg 9xx and a kenwood kvt-915 dvd, after applying the hack and putting everything back on when the unit is in harddrive scan when it selects the next son its kinda skips right at the beginning!
I have this problem with one of my hacked drives, but not the other hacked drive. it is very odd.
Make sure that logging is not turned up.. you can check the rc.sh file and make sure logging isn't set to anything above a 1, or just extract the rc.sh and rc.sig from the firmware files for your DMS and replace the ones in phtsys ... I haven't tried fixing the stuttering yet but I believe that is my issue right now.
please state the make and model exactly of the drives that experience this issue in case it is a hardware compatibility issue of some kind.
If you ran the verification process after the hack, then the original RC pairs should have been restored.
After running the hack using the DMS tools you should run the Hack Wizard again and this will undo certain bits to put your DMS pretty much back to how it was before the hack was put onto it.
(Pretty much meaning it just re-modifies some of the files it replaced/altered)
As Jud says, if you didn't do this, you will have the full Level 10 logging RC pair, so this is likely the cause.