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Old 07-29-2009, 01:36 AM   #1
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Attic fan motor rattle


I just replaced the motors (3.1 amp, 120 volt) in two attic fans. Both are hooked up to thermostats and worked beautifully for the first week. Now, both are still working but one is making a pinging/rattling sound after about 7 days use. I assumed the fan was loose on the shaft or that the fan blades were hitting something, but I pulled off the cover and saw that the fan is spinning perfectly, not hitting anything. I checked the tightness of the fan on the shaft and it's tight as can be. I can't figure out where this sound is coming from -- any ideas? Maybe it's the power conduit flex or something? Help!

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Old 07-29-2009, 06:51 AM   #2
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Attic fan motor rattle


Fan blades often contort and grow while running. Check for something close to the ends. And they will suck things up from below, cobweb, piece of string, etc.

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Old 07-29-2009, 08:23 PM   #3
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Attic fan motor rattle


Just Bill is right. Attic fan blades do grow or something, and only when you are not looking at them to see what the heck is going on. I installed on early last spring and the lady called me within a week to tell me there was a noise in the attic every day about 11:00 a.m. I go over and stand in the tight attic, in the heat and watch the fan when it comes on- -no noise. As soon as I let the folding attic stairs up the noise starts, fold down the stairs and it stops. Is it the stairs? No, it was the extra air drawn in from the attic stairs being down that quietened the fan. I went back up, let the lady put the stairs back up and the noise started. After stopping the fan and adjusting the blades just a little, a few times, I got the noise stopped. Strange things happen in some homes. Thanks, David
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Old 07-29-2009, 09:24 PM   #4
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Attic fan motor rattle


I've seen this with computer fans, the shaft can move a bit up and down, and it may move differently based on the static pressure. Not sure about attic fans but often noise issues with computer fans are related to bad ball bearings, or not enough lube. The blades on bigger fans can also expand a bit due to centrifugal force so maybe they're rubbing slightly on the casing, and only do it depending on the shaft position. A shaft that moves too much usually indicates an issue as well, but it's normal for it to be slight play (very small).
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Old 07-30-2009, 02:24 AM   #5
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Attic fan motor rattle


I appreciate the feedback -- I plan on going up on the roof and taking off the fan blades to see if it's the motor. If it doesn't make any noise with the propeller off, I'll tweak the blades as you recommended and see if that helps. I'll post to let you know how it all went. Thanks all!
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Old 08-02-2009, 06:15 PM   #6
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Attic fan motor rattle


OK, so I went up and took off the propeller and as expected, the noise stopped -- the motor just hummed along beautifully. So I took the propeller and was working with it to make all the blades level as possible and I went back up and installed the propeller, then came back down to turn the motor on, to realize that I'd left the motor on for about 15 minutes with no propeller on it running, and now it was stopped! I reinstalled the propeller and the attic fan "cap" but here we are an hour later and it's still not turning on. I've tripped the breaker a couple of times to "wake it up" but nothing. Do these motors overheat in direct sun without the fan to cool them? Hope I didn't ruin it!
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Old 08-02-2009, 07:47 PM   #7
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Attic fan motor rattle


Quote:
Originally Posted by Thurman View Post
Just Bill is right. Attic fan blades do grow or something, and only when you are not looking at them to see what the heck is going on. I installed on early last spring and the lady called me within a week to tell me there was a noise in the attic every day about 11:00 a.m. I go over and stand in the tight attic, in the heat and watch the fan when it comes on- -no noise. As soon as I let the folding attic stairs up the noise starts, fold down the stairs and it stops. Is it the stairs? No, it was the extra air drawn in from the attic stairs being down that quietened the fan. I went back up, let the lady put the stairs back up and the noise started. After stopping the fan and adjusting the blades just a little, a few times, I got the noise stopped. Strange things happen in some homes. Thanks, David
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Old 08-11-2009, 12:09 PM   #8
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Attic fan motor rattle


Just wanted to post a final update for posterity -- no matter what I did, the motor did not want to work, I guess it was just defective, so I took it back to the store and got a new one. Upon installation, the fan rattle started again so I took the advice given on this thread and played around with bending the blades a bit. It took about 15 minutes of tweaking, starting up the motor (using the thermostat switch), then tweaking again but eventually the rattle disappeared! Seems like the blades needed to be "flatter" (less pitched) and that took care of it.

Typically, though, now that that one is quiet, the other one is starting to make noise! I'll go up and do the same tweaking to it, but if this continues, I'm just going to replace the propellers and move on with my life!
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Old 08-11-2009, 01:38 PM   #9
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Attic fan motor rattle


You might press on parts of the fan's frame or grillwork to see if you dampen the rattle and thus narrow down on where the rattle is.

Bending the blades to reduce their pitch will also reduce the air flow.

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