XM '98 A/C sound

[nino1]

Hi, i have started to be a strange "gargling" sound when i turn on the automatic A/C in my mk2 XM.
With the A/C on there is aprox. some 20-30 secs of silence, then a "power-up" sound the some 20 secs of muffled gargling sound then a "power-down" type of sound.
This goes in cycles while the A/C is on.
On the other hand the output is fine.