We recently had a RadonAway 501C fan installed for sub slab depressurization in our 1923 Cape. Our readings dropped immediately from 6 - 13 (average 9) to 0.3-1.5 (averaging 0.7)

We did expect that the fan would make noise - especially as it is a "high suction" at just under 4"wc. And indeed, the noise of the pipe in the basement is not unpleasant.

However we do get an additional rhythmic/reverberating woo-woo-wo-wooo. It's not obnoxious like the videos I've seen of 10 year old fans with toasted bearings, but it is super annoying - especially at night in our very densely developed neighborhood.

I liken the noise best to blowing over the opening of a bottle or jug.

It is very regular and does not appear to be tied to wind or weather, though it might be slightly more noticeable when it's raining.

It seems to originate outside as it is very faint in the basement, but very noticeable in the second floor bedrooms which are effectively at the same level as the exhaust as the rooms have slopped ceilings.

The installer came back with a cheap muffler (3" diameter pipe lined with 1/4 or 1/3 inch black foam) it made it slightly quieter but honestly not in any meaningful way.

What might be causing this reverberation"woo-woo" and how might I address it?

  • I would think you could dampen the noise by ensuring that any clamps holding the exhaust line are rubber/foam insulated to isolate them from any vibrations that may be induced by the fan.
    – FreeMan
    Oct 6, 2021 at 16:29
  • @FreeMan, good tip but the mounting is all done with neoprene spacers and placing my hand on the fan and pipe I can hardly feel any vibration anyway. this really seems like its air flow related to me
    – Zipper1365
    Oct 6, 2021 at 16:43
  • Does shutting the fan off temporarily at the breaker make the noise stop? Oct 7, 2021 at 1:09
  • @ThreePhaseEel the noise starts back up as soon at it gets back up to speed. If you had thought it might be an electrical noise, my gut says no but I'm certainly no expert.
    – Zipper1365
    Oct 7, 2021 at 23:34

2 Answers 2


I reached out to the installer after swapping out with an identical fan myself (which was later returned).

The noise was present in both the original (Radonaway501) and the replacement, so I reached out to the installer who admitted that I was not the first with the exact same description of the noise. In fact all similar complaints were for installs around the same time.

The noise was distinctly NOT a defective bearing, but rather the installer hypothesized the impellers or housings from this entire production run may have been defective leading to flow turbulence.

They swapped out for a GX5a fan and it runs quieter than I expected a radon fan could and with better mitigation readings to boot.

  • Most of the time this noise is caused by the bearing in the spin module.
    – DMoore
    Dec 2, 2021 at 19:06

Asking why the noise is so loud is like asking why a trumpet is loud. The tube amplifies the vibration.

Moving air is noise, so you can't expect it to be dead silent. But, if the noise is loud then something is wrong.

If the muffler did not reduce the sound a lot, then it is highly likely that you have a bum fan whose bearings were bad from day zero. I doubt that there is any kind of restriction or whistle in the pipe.

  • right, so it's not so much that the the air flow noise is the problem for us- that is what it is and we have neighbors with similar set ups that sound like one would expect a fan to sound. Rather it seems that something else is mildly resonating beyond that noise of the airflow. all I can think is that it has to be bearings since it is so regular - it must be tied to the rotation. I was specifically wondering if there could be something wrong with the install that would cause such a whistle so its good to hear to suspect that is unlikely.
    – Zipper1365
    Oct 7, 2021 at 23:32

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