Phantom ultrasonic sensor response?

[Lunares]

My ultrasonic sensors have been acting up a bit lately. Occasionally (even while driving) they will flash red and show the "stop" warning as if something was <10" away from me (front or back). But there's nothing there. It then goes away and doesn't cause any more issues, but it's kinda annoying since it beeps.

Any idea what could cause the ultrasonics to trip when nothing is present?

 

[henleyregatta]

I understand they're sensitive to muck or snow/ice on them so if they're dirty that might do it?

If one or more has become mis-aligned in any way (e.g. pushed in) you might be getting "phantom returns" from bits of bodywork the signal's bouncing off, but in both cases a visual inspection should be fairly easy and quick indicator of any problems...