Unexplained radio issue - or do you know better?

[Simon]

Last month I travelled in and out of Rennes, arriving on a Friday and leaving on a Saturday. On arrival after checking the ATIS I dialled into the approach frequency on my 430 to be met with loud, high pitched white noise. This noise stopped each time someone used the frequency, including myself, so communication was no issue but the noise in between was disconcerting to say the least. I was handed over to Tower and the problem went away. The next day the same thing happened. As I went from tower to approach the loud, high pitched white noise returned. And when finally I went from approach to Brest information (stop sniggering at the back!) all was fine and nothing like it has been heard since. I have 2 boxes and tried it on each and it was the same.

Any thoughts as to what might be happening there?

[simon_gci]

Down here in Guernsey last week, the high pressure was causing lots of breakthrough and white noise on the tower frequency, sometimes would here transmissions breaking through for Blackpool approach (which is the same frequency as Guernsey tower), maybe you experienced something similar

[Ted.P]

I've had the same thing with a 430. I was listening to ATIS and pressed the vol button to stop auto squelch as the signal was weak. When I switched freq I got white noise because I'd forgotten to press the sqelch button again. This would produce exactly the symptoms you describe, although I'd have thought you would remember pressing the squelch button again - so perhaps there is some other reason. But auto-squelch disable sounds the most likely.

[The Westmorland Flyer]

It sounds like the squelch is being lifted, possibly by some low level noise on the frequency. There will be a way to make the squelch less sensitive but that is probably not advisable unless the problem is occurring often, in which case your avionics man will be able to make the adjustment.

[peterh337]

Did it happen on other frequencies?

I got this kind of issue with having too-well lubricated (as if there was such a thing) elevator bearings, and the static could not make its way across them to the elevator static wicks, and was arcing across them, creating a lot of interference on the radio.

COM2 was a lot worse than COM1, as the COM2 antenna is a lot nearer the elevator.

I solved it by adding two bonding straps, between the elevator and the hull. Two, in case one came off.

Or it could be something in the cockpit; some portable device perhaps?

[Simon]

I hadn't thought of the squelch button - probably because it hadn't ever happened before or since. But will check if it happens again.
Peter - as mentioned, it was only on the one frequency and has never happened since so I'm relieved to think I don't have to consider your remedies!

[Keef]

I've had this a few times. In my case, it was caused by the local oscillator of the NAV receiver happening to be on a frequency which offended the COM receiver and therefore opening the squelch. Changing the frequency set on the NAV made the noise go away.

If I could remember where it happened, I could probably say which VOR frequency interfered with which Approach frequency, but memory isn't that good.

[Paul_Sengupta]

Indeed, sounds like interference, either internal or external. Did you try tuning into that frequency again when away from the original area? Expanding on what Keef says, did you try tuning in all the same frequencies on all the boxes somewhere other than the original area?

If the interference is present when away from the original area when all the same frequencies are tuned in, then it's within the aeroplane and you might have to tune one of your nav boxes away from the frequency it's on.

My bet is it was something in the local area.

[Simon]

That's a good point. I haven't checked that frequency since being back in the UK.
I will try when next up and report back. Thanks all for the ideas.