When it gets really cold around here, below zero, and there is visible moisture in the air, when I drive my patrol vehicle a haunting tone occurs between certain speeds, roughly 40 to 60 mph, but the speeds change with conditions. Not sure if the visible moisture is important, but anytime I've heard it there was visible moisture. I've never noticed this in my POV so I'm not sure if it has something to do with the radio or the light bar. It's happened in multiple patrol vehicles.

Anybody have any ideas?

Is your patrol car AWD? What is it? Not saying this is the reason just thinking

I’d guess ice build up on the antenna making the sound. In railroad vehicles with the long 3” antenna we used to notice a hum at certain speeds and certain conditions.

It's a 2020 Ram 1500. I've also heard it driving a 2015 F150. Both were 4x4s, but not AWD.

@SigM4

Is the antenna itself making the noise or is it coming through the radio somehow?

The seal around the windshield is shrinking in the cold.

quote:

Originally posted by mark123:
The seal around the windshield is shrinking in the cold.

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It likely would not happen in 2 different vehicles.

It has something to with you radio or emergency equipment.
What exactly way too many variables to know.

I remember working 3rds my equipment would make some weird noises at times.

Not trying to be funny, but what is “visible moisture in the air”? I have no experience, but at below zero wouldn’t any moisture be ice?

Certainly any ice buildup on the vehicle would result in different sounds at various speeds, whether on the grill, antenna, or light bar.

Mostly freezing fog.

If the sound changes at different speeds in different weather, I'd look for ice buildups that change the wind noise.

Freakin' elves, man

Quite possibly ice build up on your antennas.

Trunk monkey getting cold?

I put a 2M antenna on my truck about ten years ago and noticed the same problem, although mine was all the time and not just when moisture was in the air. What I did was wrap the antenna with black electrical tape (just spiraled it up in one layer). Solved the funky noise issue at speed and didn't affect the Tx/Rx at all.

I’m going with light bar. I bought a Subaru that I anticipated replacing a wheel bearing. I removed the after market roof rack and voila, the noise was gone.

quote:

Originally posted by honestlou:
Not trying to be funny, but what is “visible moisture in the air”? I have no experience, but at below zero wouldn’t any moisture be ice?
<snip>

Actually, microscopic moisture particles in the air can remain liquid at below-freezing temperature.

But when the air is disturbed by a rapidly moving vehicle those particles can suddenly freeze on to the vehicle. A hazard well known to pilots.

quote:

Originally posted by Pipe Smoker:

microscopic moisture particles in the air can remain liquid at below-freezing temperature.

But when the air is disturbed by a rapidly moving vehicle those particles can suddenly freeze on to the vehicle. A hazard well known to pilots.

The V-Tail had a whip antenna, maybe three feet long, mounted on the cowling in front of the windshield. I thought of it as my "ice detector." I normally never noticed it in flight, but the antenna was the first thing on the airplane to accumulate ice, which unbalanced it, and the antenna would whip back and forth. That motion caught my eye, I would then look at the leading edges of the wings, and sure enough, every time, there would be ice starting to form.

Something related to air density and maybe some ice causing an acoustic vibration. Weird.

Our home furnace does that too, with high humidity and temps in the upper 20's. It has an air intake from outside, a 3" plastic pipe, and next to it the exhaust air, also a plastic pipe. It makes an owl like hoooing noise. I assume ice in the intake.

quote:

Originally posted by Skull Leader:
It's a 2020 Ram 1500. I've also heard it driving a 2015 F150. Both were 4x4s, but not AWD.

@SigM4

Is the antenna itself making the noise or is it coming through the radio somehow?

It’s the antenna itself making the noise at speed. The radio is off when this happens.

The Ghost in the Machine! LOL

The most noise from any of the patrol cars I ever drove came from the lightbar mounts.