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My wife says I have bat hearing and I can hear CRTs, capacitors charging and all manner of things that humans aren't supposed to hear. I figure this "ultrasonic" sensor is just more of the same.
We initially got around the problem by putting a wide piece of tape on the edge of the center ultrasonic sensor. I used 2 or 3" gaffers tape with just the edge of the tape on the plastic part of the sensor and it was enough to block the signals. This decreased the issue enough that the noise didn't bother her much and riding in the car with her hearing aid in was OK (for a while before this she'd just take the aid out).
Then a few months ago she got an newer model hearing aid (same company) and the new one doesn't have any issues at all. No need for the tape nor anything else. So this appears to be very dependant on the model of hearing aid.
We have a 2006 XJ8 VDP and the 92 XJS convertible. The 2005 VDP was ruined in a hail storm while parked at Greenville Spatanburg Airport a couple of years ago.
I see from other posters it's gaffer tape. I bought a roll on Ebay and using the above diagram have covered all three sensors on the passenger side of our 2006 XJ8. Now I've got to entice my wife into it to see if the tape works. I'll let you know.
As I mentioned in a 2015 post, a newer model hearing aid from the same brand (Audibel/Starkey) solved the problem - although that's not why we got the newer hearing aid.
Since then my wife got a Widex Fusion 2 hearing aid a few years ago. I think that one does pick up the signals a little but it was so little that it didn't bother her enough to tape up the sensor. I think she also might have tuned it out with some adjustments that were available on the iPhone app for that hearing aid.
So it hasn't been an issue since our 3rd back hearing aid was retired in 2015.