Strange sound of fuselage under 3000 feet.

[Danb]

Stupid question for Acclaim pilots, my Acclaim on climb out until 2-3000 feet and in cruise under 3,000 feet my plane has a strange hum or weird sound, I’ve had four Mooneys over 35 years this is the only one with an strange sound. I’ve had the plane for a couple years, any others have similar sound. It’s difficult to describe a noise.

 

Dan 

[N201MKTurbo]

What frequency is the hum?

 

[Danb]

Good question, high 

[N201MKTurbo]

I asked because you could have some space in the plane that is acting like a Helmholtz resonator. My truck will do that if I open a rear window while driving down the freeway. It makes a very low frequency, actually subaudible, sound. 
 

If you are getting a high pitched sound, it could be a piece of sheetmetal or an antenna vibrating in the wind, or a small cavity whistling. 
 

A recording would be nice.

[Danb]

I was thinking something like that, I’m going to make sure the gear doors are fit good and go from there..it is somewhat high pitch but disappears around 2000+ feet.

[N201MKTurbo]

Check the sheetmetal covers on the tail. Make sure no screws are missing.

[Schllc]

1 hour ago, Danb said:

I was thinking something like that, I’m going to make sure the gear doors are fit good and go from there..it is somewhat high pitch but disappears around 2000+ feet.

I’m betting it’s your door seal. My climb rate is usually declining by 3000’.  
tear a bunch of strips of paper and when you start hearing the noise, move the paper methodically along the door seam. The scrap will stick where there is a leak. I’m betting you will find your noise eliminated…

[Danb]

Ray I wasn’t thinking door which makes sense I think I’ll get painters blue tape and tape it from the inside and go for avride

 

TY

Dan 

 

[LANCECASPER]

18 hours ago, Danb said:

Ray I wasn’t thinking door which makes sense I think I’ll get painters blue tape and tape it from the inside and go for avride

That also makes sense since you had an inflatable seal on your last airplane, so not having one on this airplane would make the sound seem different. 

[cbarry]

My first thought is an item that changes in size based on heat expansion such an exhaust and/or turbocharger system component and that by the time you’re above 3000 ft., there’s been enough heat expansion to either tighten up the tolerance or at least change the frequency enough that it’s not as noticeable.  My second thought is an alternator diode going out  (if it’s noticeable through the audio system). My third thought is a slight engine and/prop vibration resonating through the engine mount into the cabin’s steel cage—almost like a tuning fork would act.