Replaced an old unit for a new 16.5 seer 401a system.Very quite operation.Florida weather has been cool,so we haven't used it much.However,today I was doing a little yard work when the system turned on.Now I'm so used to the old A/C which was loud.But I did hear a start up buzz/click(like a contactor)hum, and after a few mins the 'sound' sort of evened out to a fairly low audible buzz.Is this normal in start up? Please inform and thanks...