"hoot" sound from engine compartment-- a/c ?

[Todd H.]

Got a weird one here.

I'm hearing an intermittent "hoot" sound that is higher in pitch than
an owl would make. Probably in the ballpark in frequency of the tone
that's played with color bars on a TV set/station test pattern (1kHz).
If I had to guess, it's probably aroudn 700Hz. It doesn't last long,
maybe a second, at most I've heard it for 4 seconds continuously.
Crops up once every few minutes at most, seemingly randomly.

I've heard it happened while:
stopped and idling,
coasting at low speed,
starting off and going up a hill
and ... here's the one that gets me:
even JUST after the car has been turned OFF.

Seems more frequent on hotter days.

Doesn't seem to vary with wheel speed or engine speed.

I've not yet heard it when the Air conditioning is off (but I just
tested this on 2 drives yesterday after the idea came to me). The A/C
system was serviced about a month ago. So my best guess is the air
conditioning system somehow.

What in the A/C system might cause such a noise I wonder? Or how
could someone addressing a cooling system leak have screwed up to
cause this to happen?

Or could it be something else still? Alas, I could not find an owl in
the engine compartment to explain it otherwise.

 

[1 Lucky Texan]

Got a weird one here.  

I'm hearing an intermittent "hoot" sound that is higher in pitch than
an owl would make.  Probably in the ballpark in frequency of the tone
that's played with color bars on a TV set/station test pattern (1kHz).
If I had to guess, it's probably aroudn 700Hz.   It doesn't last long,
maybe a second, at most I've heard it for 4 seconds continuously.
Crops up once every few minutes at most, seemingly randomly.

I've heard it happened while:
     stopped and idling,
     coasting at low speed,
     starting off and going up a hill
and ... here's the one that gets  me:
     even JUST after the car has been turned OFF.

Seems more frequent on hotter days.

Doesn't seem to vary with wheel speed or engine speed.

I've not yet heard it when the Air conditioning is off (but I just
tested this on 2 drives yesterday after the idea came to me).  The A/C
system was serviced about a month ago.  So my best guess is the air
conditioning system somehow.

What in the A/C system might cause such a noise I wonder?  Or how
could someone addressing a cooling system leak have screwed up to
cause this to happen?  

Or could it be something else still?  Alas, I could not find an owl in
the engine compartment to explain it otherwise.

Does it sound like your security system beeper?

 

[StephenH]

Got a weird one here.  

I'm hearing an intermittent "hoot" sound that is higher in pitch than
an owl would make.  Probably in the ballpark in frequency of the tone
that's played with color bars on a TV set/station test pattern (1kHz).
If I had to guess, it's probably aroudn 700Hz.   It doesn't last long,
maybe a second, at most I've heard it for 4 seconds continuously.
Crops up once every few minutes at most, seemingly randomly.

I've heard it happened while:
     stopped and idling,
     coasting at low speed,
     starting off and going up a hill
and ... here's the one that gets  me:
     even JUST after the car has been turned OFF.

Seems more frequent on hotter days.

Doesn't seem to vary with wheel speed or engine speed.

I've not yet heard it when the Air conditioning is off (but I just
tested this on 2 drives yesterday after the idea came to me).  The A/C
system was serviced about a month ago.  So my best guess is the air
conditioning system somehow.

What in the A/C system might cause such a noise I wonder?  Or how
could someone addressing a cooling system leak have screwed up to
cause this to happen?  

Or could it be something else still?  Alas, I could not find an owl in
the engine compartment to explain it otherwise.

sounds like the AC, have had funny sounds when overfilling the a/c
system; id take it back and have them evac and recharge the a/c system

 

[rss1]

sounds like the AC, have had funny sounds when overfilling the a/c
system; id take it back and have them evac and recharge the a/c system

AC, I just finished fighting the same thing. A little too much gas in
the system

 

[Todd H.]

Does it sound like your security system beeper?

I dont' have one, and nah, it's not electronic sounding at all.

 

[Todd H.]

AC, I just finished fighting the same thing. A little too much gas in
the system

Cool. That makes sense to me. Thanks for the datapoints! Knowing
what it is makes it a lot less annoying.

Think there's any long term system health issue of leaving it as is?
I may do that if it stays as infrequent as it is (haven't heard it for
a week).

 

[rss1]

Cool.  That makes sense to me.  Thanks for the datapoints!   Knowing
what it is makes it a lot less annoying.

Think there's any long term system health issue of leaving it as is?
I may do that if it stays as infrequent as it is (haven't heard it for
a week).  

No big issue with a little too much gas, but the system works cooler
with the right amount. Gives room for the gas to expand (cool) in the
evap.