Long delay when auto attendant transfers to external extension

In auto attendant when caller presses option to transfer call to external extension there is like 15 seconds delay with pure silence before the call is initiated. How can I remove that silence, can I add "Music on Hold"  or something like "We will try to locate your party". I am afraid the silence will make the caller hangup.

Using FVe-20e4 with firmware 6.4.4. Thanks