Wire-Lists #33: Hey! What's That Sound?

Social Media WireLists33 300pxTroubleshooting Possible Reasons For What You're Hearing

Our Service Department are like mechanics in that we frequently get calls that start with, "I turned on/was using my (product) and heard this sound..." This list will discuss the types of sounds you might hear and give you some examples, along with what you can do to help figure the root cause/s of the issues.

In order to help troubleshoot, we need to know (or you need to consider):


  1. What were you doing? Specifically, we need to know what happened proceeding the sound. Did you just turn the unit on? Was it working normally prior to when you heard it? Is the sound coming from your transmitter or your receiver…or are you not sure because you are hearing it in earphones? Is a mic attached? Did you hear the sound once, or is it intermittent or constant?
  2. What is the application? How are you using your equipment, and in what environment? With a mic or without? What frequency are you using, and is there other equipment working with it or near it?
  3. Have you ruled out ambient noise? Occasionally and especially if you are working in a noisy/busy environment or one that you know has a great deal of interference, you’ll want to ensure that what you hear is really within the equipment and not outside.

To follow are seven scenarios that you might experience. Please note that these are not absolutes, and what you hear or experience may differ. We share these because they are indicative of the nature of a particular situation and give you a good starting point on what to look for:

1) 2.75k whine/warble with SMWBs (including SMDWBs)

There are two types of sounds that may indicate a problem with your transmitter: a whine and a low-pitched warble. The whine is triggered by the Remote setting (i.e. “RC ON”). The warble is triggered by using a frequency evenly divisible by 12, which we explain in a bit.

The Whine

The graph below shows the “Remote” noise as a 2.75kHz whine and it appears on all frequencies. This clip is what it would sound like:

SMWBE07 SN 125 whine

The fault goes away, as you can see and hear, if the Remote is set to “RC OFF”. This graph shows the results of this remedy, as well:

SMWBE07 SN 125 no whine

If you have units with this issue, we have a fix! Please reach out to our Parts & Repair department at 800-821-1121 or This email address is being protected from spambots. You need JavaScript enabled to view it..

The Warble

As previously mentioned, the warble appears on frequencies evenly divisible by 12. A1 frequencies that will have this issue are: 480.000 MHz, 492.000 MHz, 504.000 MHz, 516.000 MHz and 528.000 MHz. B1 frequencies that will have this issue are: 540.000 MHz, 552.000 MHz, 564.000 MHz, 576.000 MHz, 588.000 MHz, 600.000 MHz and 612.000 MHz (EU only) No other frequencies exhibit the warble. We contacted customers for whom this might be an issue and retrofitted their units with an internal modification that we have since addressed in the fabrication process for units manufactured recently. If you have had your unit for a few years and it has not been modified and you are experiencing whines or warbles, contact our Parts & Repair department to ask about it at 800-821-1121 or This email address is being protected from spambots. You need JavaScript enabled to view it..

2) SM and variants (SMa, etc.) with a legacy mic

Are you using several SMs – some old and some newer - and you notice noise on some but not on the others? Have you had service done where the Audio/Logic PCB was replaced with the newer version of PCB (when used with non-servo mics)?

Some users have reported that their SM unit/s exhibit a low-level whine, and example of which you  can listen to here: 

In the example, we tested this with no microphone attached and were able to hear the whine in the audio, but had to greatly increase levels out of the receiver to hear it. However, the whine with no microphone attached also went away if the Remote was set to Ignore.

The reason for this happening has to do with the servo bias input circuit wiring and the difference in specs between the voltage offset parts. In late 2018, we changed the op-amp in the servo bias input from SIA7301 to SIAAD8605, which in turn changes the wiring method.

The older, non-servo wiring method is:

When we changed to SIAAD8505, the following changes were made to the older method:

For the units that are exhibiting the error, you will need to switch to a different mic, or have your ground shield wired accordingly. We cover 5 input jack wiring in our Support article on wiring.

3) Signal to noise ratio and the noise floor (audio gain and gain structure issues)

Signal to noise refers to the relationship between how strong the useful signal is verses the noise you don't want, and noise floor refers to how strong the noise is. In any system, you will also have some level of noise. Your device interprets signal quality through the signal to noise floor. Input gain is the most important adjustment on any wireless system, and the gain must be fully modulated to give the system as much signal as possible to work with. Gain that is too low accounts for the majority of noise complaints that we receive. The following resources will help you correctly establish gain structure: *Tech Note 1016: Transmitter Audio Gain vs Signal to Noise Ratio

4) Antenna Whip (or Slap) in Transmitters

All transmitters have some antenna whip (movement) noise. If it sounds excessive, you can run the following test:

  1. Attach a microphone and set your gain with a voice test until you have full modulation on the transmitter;
  2. Monitor the output from the receiver with the audio at a comfortable listening level;
  3. With the microphone attached but with no audio source, move the antenna back and forth about 45° from vertical and monitor the audio or noise. Do not increase the gain or monitoring level;
  4. If moving the antenna causes the receiver modulation to vary beyond ¼ full scale, the unit suffers from Antenna Slap.

A transmitter exhibiting Antenna Slap that you cannot fix by trying the above suggestions requires an RF board replacement to fix, which we or an Authorized Factory Repair shop can do.

5) Theremin Hum

Theremin hums are another antenna-related error in transmitters that is not common, but they happen and are very distinctive. You’ll notice it when you move your hand near the transmitter – it will make a low-pitched, variable hum, inversely relative to how close your hand is. Imagine it as the “power” sound that was used in old Sci-Fi B movies. It is caused by spurious emissions, which are harmonics or other signals outside a transmitter's assigned channel. A transmitter that is exhibiting a Theremin hum needs to return to us for service.

6) High Frequency Whine With Power Supply Bricks

This can be heard in the power supplies for the DSQD, M2T and Venue 2). Users sometimes mistakenly think that the sound is coming from the transmitter or receiver, when it’s actually coming from the power brick. The way to test this would be to try another power supply – or a different, compatible type. If the sound goes away, there’s your answer! If this isn’t a possibility, place the power brick in a different location, ideally on the other side of your cart, or further away in the rack.

7) Bad Regulator

This is a rare one, but it happens, especially in units that are older and have had a long use life. We build products to be very durable and have had many units in the field for 20+ years, but like everything else – cars, appliances, and yes, even the human body – units wear out and show age after a while. A receiver with a bad regulator will release an intermittent sound that changes pitch, similar to a Theremin hum. Units with bad regulators are easily repaired but would need to be sent in for service.

Sound issues can be tricky to diagnose, but we’re always here to help. This email address is being protected from spambots. You need JavaScript enabled to view it. or post a question on our Facebook group, which always has a few active threads from other users, trying to troubleshoot sound anomalies. Remember, also, that like doctors, we have to evaluate the entire system to diagnose and repair issues. If you send your unit to us or an Authorized Repair technician, please remember to include the microphone, power supply and any wiring so that all parts can be tested.