Mysterious Audio Noise

A few weeks ago, while passing through KC center, I was on 132.7. On both Garmins, this distinctive rythmic sound was in the background. It wasn’t center’s problem, but mine.

Went to Business Aviation in FSD (a SC) and our trouble shooting ruled out the Garmins. Ended up being the EMAX module. Am waiting for a replacement now. What was strange was that it wasn’t on any other freqency that I could tell. It also initially sounded like it might have been bleed over from a mag or alternator.

Just thought I would pass this info along.

David Schwietert 203 RF PFD/TKS/Emax/Skywatch/Stormscope

I’ve had something that sounds similar, but on 126.85

When you say the EMAX, do you mean the SIU (sensor interface unit)?

Please post when you have that replace, if it resolves the issue.


Are you sure it wasn’t Denver center? I had this exact experience on 132.7. How did you discover it was the SIU?



You indicate that you “had” a similar sound. Now you don’t? What fixed it? Did it just go away?

I believe that it is the “SIU” which is located above the right front passengers knees and dash, underneath the plastic cover.

I will keep you posted as to the end of the story.

Flying Safely,

David Schwietert 203 RF PFD/TKS

I wrote “had” because when I changed frequencies, it went away :slight_smile:
I believed it to be an aircraft noise problem, rather than noise being received
by my radios, because I found if I turned off Garmin #2, the noise went away
on Garmin #1, yet the noise always showed up on Garmin #2, whether
Garmin #1 was on or not.

I don’t use that frequency much, and I have’nt noted this issue on any other
frequency, although I’ll try the 132.7 where you’ve noted a cyclical noise pattern.



Now you got me thinking and I think you may be right. Switched from Denver Center 127.95 to 132.7. The next hand off was KC Center. Good Catch.

Our first inclination was something related to the alternator or Mag. I first only noticed it with engine power (flying). Just before visiting my SC, I turned on the battery switch and then avionics. Turned to 132.7 on both radios and there it was. So, it was not connected to any electrical interference caused by the running engine. An astute mechanic and avionics tech. next had the idea that it might be related to the emax, since nothing else was on. All other possible related CB’s were also pulled with no affect.

Once we removed the plastic knee shield, we then pulled (one at a time) the plug-in bundles (there are 2) and one of them cancelled the cyclic sound.

Hope that answers your question. Waiting now for the new SIU. Will keep you posted.

David Schwietert 203 RF PFD/TKS

Thanks for the info. I’ll see if I can replicate your results today.


Tried 132.7 again on the ground, and experienced the same rhythmic sound. Pulled the EMAX breaker- no sound. After calls to Cirrus and Avidyne they say that this is a known issue and to expect an SB within weeks. This will involve adding some type of filter to the SIU.


In reply to:

This will involve adding some type of filter to the SIU.

In reply to:

You mean those weren’t actually used on the old coffee grinder radios…?

  • M.