I have noticed over the last week my AC compressor is very noisy. I can hear it cycling when sat stationary. It's making those fridge noises; bit like the sea over pebbles. If I turn off the AC but leave on the fan it stops. 

 

It blows nice and cold and clears the screen well. Not sure if it something to be concerned about or not. 

If it sounds different, i.e. significantly louder then don't use it. Have it checked out and if it's on the way out, you may save further damage to the other AC system components and only have to renew the compressor.

It could be low on refrigerant

I said in another post as well
 
Try Groupon loads of cheap deals this time of year. I got my Merc re gassed for £18 locally 

probably bearing gone, may seize

If it sounds like flow nose then I'd start with a re-gas.

Just to add my scenario, my A/C also makes some unusual noises, much like you describe. I too suspected low gas.

 

This was back when my car was in warranty, the dealer checked it out and simply advised a re-gas. Had this done, no difference, still noisy.

 

That was a few years and 50,000 miles ago and it's still making the noise but still working fine.

 

Thing is the noise is intermittent so difficult to replicate when you need it to. Turning the A/C off stops it instantly.