Records are normally automatically added to the zone when computers and domain controllers are added. In some cases, they are not automatically deleted. This are stale records.
Windows DNS server can “scavenge” this records.
Scavenging settings on a Resource Record
Goto DNS – click View -> Adcanced -> Klick on the properties of a record.
“Update associcated pointer (PTR) record” is a useful setting. Without activating it, every time the IP for a client is changing (because of DHCP), there will be a new entry in the reverse lookup zone.
Scavenging Settings at the Zone
Klick on the properties of a zone and klick “aging”.