Delay answering a parked call?

I've noticed in the office more and more "Hello? Hello?..." when someone picks up a call from the parking lot.

When retrieving someone from park, I press a blf key to pickup the parking slot

topsoftkey1 type: blf
topsoftkey1 value: 71#

The # sign helps to speed up the connection process, but I still find a delay in how quickly the other party can hear me.

Is there anything else that can be done to speed up the connection process?

(My hunch is that the music on hold volume is too loud, and the callers hold their earpiece away from their ears while we have them on hold)

Thanks