Having a annoying problem here....

When someone does a station to station intercom call using * and then the extension, after the calling party hangs up, the destination phone will ring 3 times.

Example: Extension 19 calls extension 11 by dialing *11 or by pressing a programmed button. After extension 19 hangs up, extension 11 then rings 3 times with 2 short beeps between each ring.

Anyone know how to stop this?