Weird A/C Noise - Coil Type AC

[ypw]

I have noticed that about an hour after shutting off the A/C, the compressor unit makes this cranking sound. It is rather loud (almost sounds like a howl), and it stops by itself in about 5 minutes. If I turn it on while it is making this noise the noise goes away.

Anyone with ideas about what this might be? Cooling seems to be okay.

Thanks!

More info:

I was told today by a technician that this noise is normal for a coil type air conditioner. Has anyone heard about noises specific to coil type a/c?