We have a swamp cooler (evaporative air) for cooling, and forced air gas furnace for heating. There is an irritating squeal coming out of the vents when the swamp cooler is running. It is not consistent, and seems to stop or lesson when we run water or take showers. With evaporative air, we can turn the pump on which adds water to the pads, or we can just turn on the fan for air alone. Either way, we have heard the noise. I believe the problem is with the air vents themselves somehow, and not the cooler, because one night the swamp cooler was not running, but we had strong winds outside that came through the vents, and the whistling noise started. The weird thing is we replaced the swamp cooler recently with a new unit, and didn't hear the squeal for about two months. Thought it was gone for good, then out of the blue the squeal came back.
How is this happening, and how can we stop it? It is extremely annoying.

We have a swamp cooler (evaporative air) for cooling, and forced air gas furnace for heating. There is an irritating squeal coming out of the vents when the swamp cooler is running. It is not consistant, and seems to stop or lesson when we run water or take showers. With evaporative air, we can turn the pump on which adds water to the pads, or we can just turn on the fan for air alone. Either way, we have heard the noise. I believe the problem is with the air vents themselves somehow, and not the cooler, because one night the swamp cooler was not running, but we had strong winds outside that came thru the vents, and the whistling noise started. The weird thing is we replaced the swamp cooler recently with a new unit, and didn't hear the squeal for about two months. Thought it was gone for good, then out of the blue the squeal came back.
How is this happening, and how can we stop it? It is extremely annoying.
I've had squealing air vents before. I had one in my bedroom the last time I lived in an apartment. It was very inconsistent, and wouldn't have bothered me if it was loud all the time. I found it was louder when cooling instead of heating (we had a heat pump).

You can try tightening the vents from the walls and try opening or closing them a little bit. The trick is to figure out which ones are squealing and adjust them so that they're not leaking little bits of air. I find that metal vents tend to squeal if they're leaking just a little air, but will quiet down if airtight when closed or if they're open.