High pitched whistle

[Bill_Pyles]

Something tells me this phenomenon has an incredibly simple cause that I should have been able to diagnose, or else it will be a mysterious electrical issue.

I flew the airplane 8 hrs last week without any issuses and without any "whistle."

I went to start it today and by simply turning on the master switch, I got a loud, high pitched whisle that was coming from the speakers in the roof.  This was before I started the engine and before I turn on the radio/avionics.

After I started the engine, I taxied to the wash area, but the whistle persisted irrespective of whether the radio was on or off and it did not stop until I shut off the master switch.

I have no tripped breakers, no unusual voltage or amp readings and I selected and de-selected every button on the radio, but I still have the whistle when the master swith is on.

The only thing I have done since the trip is to take the upper and lower cowling off in order to tighten the right angle elbow fitting at the bottom of the sump that has an oil vent line attached to it.  I did not touch anay wiring except the landing light wires which you have to disconnect when the cowling is removed.

Any ideas as to the cause of the whistle?

[lamont337]

Is the sound similar to a stall warning sound or landing gear warning alarm? You didn't mention either in your post, so I'm sorry if you've already ruled that out. I had a rented Arrow do that to me even though I had 3 green while taxiing, ended up having a bad micro switch on the nose gear.

[kortopates]

Lamont's above reply would be my first thought as well if the noise could be from one of upto three sonalerts you have above your head for gear, stall and probably AP. This possibility would also require a fault in the wiring or a bad or out of adjustment mico switch as lamont described in order to continuously power one of the sonalerts though. Only the gear uses a beeping/pulsing sonalert, so from what you describe as a continuous "whistle" it would have to be the stall or AP sonalert.

Actually, if you have a King AP, not having the electric trim switch on will cause that, so check that first.

[Bill_Pyles]

Thanks for those are interesting ideas, Paul and Lamont.   I had not ruled those sonalerts out.  The whistle is indeed continuous.   I have to take the plane to the shop for another issue, but if the mechanics scratch their heads, then you have given me someting to suggest to them.

[Ron McBride]

Could it be the ELT?

Ron

[Vref]

Quote: Bill_Pyles

Any ideas as to the cause of the whistle?

[Skywarrior]

When the noise is present, pull out both the Gear Warning and Stall Warning CBs. If the noise stops, the problem is in either the stall warning vane assembly or the landing gear electronics.

[Parker_Woodruff]

This happened once in my M20K.  I could flip the stall switch and an additional stall horn (quieter) would present itself.  Pulling the CB eliminated the noise.

Do you have a handheld GPS wired to the panel somewhere?  A Garmin 396 came with my plane and I had heard of that causing a random issue like this on startup.

[mooneyman]

I had the same thing happen a while back. At first we thought it might be the turn coordinator going bad. After some investigation, it turned out to be a mlafunctioning alarm horn from the Davtron digital clock in the panel. 

[jlunseth]

Check your battery voltage and generator output also.  If the voltage falls to low, you will get all kinds of weird sounds.  The one time it happened to me (battery was going south), the operation of the strobes created a clicking sound through the speakers, and one of the radios was whining.

[Bill_Pyles]

Davtton digital clock---I have one of those.  I will check its CB.

I installed a new battery three weeks ago.  Voltage is normal. 

I never turn off the strobe switch or the trim switch, but I cycled both of those and it had no effect on the noise.

 

 

[Bill_Pyles]

With the master switch on, I pulled the CB on the stall horn and sure enough, the whistling went away.  I re-set the stall horn CB and manipulated the stall warning tab up and down a few times and I could get the thing to stop whistling that way, so something is not quite right with the circuitry in the stall warning system.  Thanks, guys! 

How do you get to the stall warning horn?  There is an access panel on the underside of the wing perhaps 15 inches aft----is that it?  

[KSMooniac]

Yep, that is it!  A couple years ago I had an inop stall warning and liberally sprayed electrical contact cleaner from the front and through that access panel (with a bit of contortion, a light, and a mirror) while exercising the switch/vane.  That brought everything back to life for me.  This was done *after* I changed the Sonalerts to no avail of course!  

[Bill_Pyles]

Scott---that is exactly what I was thinking, and about an hour ago (before I read your post) I bought a can of electrical contact cleaner with the remedy you suggested in mind.  Can't wait to try it.