Tjernlund Blower/fan noise only when power on, not when free spinning

[Jfranke3]

I have a Tjernlund GFK-160 blower and fan for my gas fireplace. It makes a strange noise that has a rhythm that follows the spinning of the fan but only occurs when the switch is actuall on. As soon as I turn off the power, the sound stops even when the fan blades continue to spin.

Any ideas? Is this a faulty motor?
Thanks for any help/advice!
Josh

 

[begreen]

It might be dirt or dust on the blades causing an imbalance. Try removing the blower and cleaning.

 

[Jfranke3]

I have it outside of the fireplace. It's clean and has made this noise since I put it in new a couple years ago, just never made the time to troubleshoot it. It's silent when the blades spin at any speed so they aren't hitting the housing and the bearings are fine.

Any other ideas?
Thanks!

 

[begreen]

A couple thoughts. One is that the blower wheel(s) might be out of balance. The other is that a low resonance vibration is happening due to the plenum shape, or inlet. Is there a motor speed control on the blower? If so, does it do this at all speeds or just at a particular speed?

 

[Jfranke3]

Thanks begreen! It does have variable speed control and the sound happens at all speeds. The sound is coming from the motor, not the fan area. It's strange. I can spin the fan manually fast or slow and it's silent but as soon as I turn the power on the sound comes from the blower/motor area. I don't know the proper terminology.

Thanks again for your help! I appreciate the troubleshooting very much!