|Popping scratchy noise sounds when the probe is first placed on the skin.
||Air bubbles in the gel are moving and/or popping. Hair movement can also cause these noises.
||Use a new dab of gel that looks clear, push the probe down enough so hair is immobilized, and wait a few seconds for everything to settle. If the noise is not there when the probe is clean (no gel) and suspended in the air, the Doppler and/or probe are probably working fine.
|Static when the dry probe is moved through the air.
||Loose connectors where the probe connects to the instrument, broken shield wire in the cable either at the connector or as it comes out of the probe.
||There is normally some static generated when the cable is flexed, but it isn't severe. Replace probe or get connectors fixed.
|High pitched tone and flow indicators (if so equipped) go to the extreme.
||Radio interference from a mobile service, police station nearby, even another Doppler working close by. Usually occurs near large open windows, rarely in the center of a building.
||Move the Doppler to another location away from windows and toward the center of the building.
|Buzzing noise that almost obliterates the Doppler signal.
||Electrocautery or other sparking device, bad fluorescent light fixture or neon signs nearby.
||Move the Doppler to another location away from the interference.
|Howling noise when probe is held or laid on a table with gel on it.
||Probe is acting as a microphone and you are getting acoustic feedback.
||Wipe gel from probe. If the noise does not occur without gel on the probe, it is probably working fine.