I'm getting cold air just fine -- but sometimes it makes a sound like somebody's knocking on the side of the house for about 15-20 seconds prior to startup:confused:

I initially thought it was the fan hitting something... but the fan isn't even running when the noise is occurring?

Some compressors tend to do that when they get a lot of milage,, don`t know of anything that can be done for it,, could go on like that for several years, I`d say either put up with it or replace it,, ((((you might look to see that the rubber feet it sits on are still in placethe rubber gromit that the bolt goes through that holds the compresser in place, )))),how old is the unit?

some compressors tend to do that when they get a lot of milage,,,,don`t know of anything that can be done for it,,,,,could go on like that for several years, I`d say either put up with it or replace it,,,,,,,, ((((you might look to see that the rubber feet it sits on are still in placethe rubber gromit that the bolt goes thru that holds the compresser in place,,)))),how old is the unit?

It's less than a year old... I can't recall the brand though.

Call the installer,, its should be under warranty