alrighty folks, for the life of me i can't figure this one out. i keep getting this strange "whooping" noise from my 2003 honda civic EX, but it only seems to happen when the A/C is on, and the car is typically at idle. my wife described it as if hearing a police siren being turned on only once and then back off again. it seems its random, but when it starts up it happens frequently, about every 5 minutes or so....maybe. any ideas?

 

If it's rather loud, probably the belt slipping. Check the belt and tighten or replace if needed.

 

ok so i did some experimenting and it seems the only time the noise appears is when the car is at idle. the new thing i found was that it happens ONLY when the compressor kicks on. i guess typically when the A/C is on and the car is at idle, the compressor kicks on and off every minute or two. when it kicks on, the "whooping" noise appears.

 

shot in the dark, but I'm thinking something with your AC clutch is screwy...maybe its not grabbing properly...OR it could be the belt. check the condition of your belt, and if its shot, replace it. Check the belt tension too, should be a little play, but not much.

 

man, i wish you guys could actually hear this, it really sounds like a police siren. also, i put the car in park the last time i heard it start to do this and opened the hood. the noise is definitely louder in the car than under the hood. odd...

 

Post a sound recording. Did you tighten and/or replace the A/C belt? Could be that the compressor bearing is shot.

 

How loud is this noise? If playing the radio at normal volume will cover it up, it is probably just the sound of normal refrigerant flow through the expansion valve.