Problems with Active directory server

For the past 2 months, when I restart my server (Active directory – Windows SBS 2003 SP2) and before "Applying computer settings" shows up, I get the message "Active directory is rebuilding indices" and I have noticed that the server has become slower. Is it possible to stop the automatic running of rebuilding indices?
Also at 'Services' the RPC is running with 'Local System Account'. Shouldn't it run with 'NT AUTHORITYNetworkService'?
