like hissing noise
 

2009 Honda Civic LX. When I start the engine I have this noise and slowly will go low and so,metimes it will go back like it want to speed up and then goes mellow again and sometimes it goes away and come back again ... another thing is that when my ac clutch is engage it will go away sometime and be back again.... I apologize for this description but then I notice that when I turn off the engine I can hear alsmost the same sound. I change my tensioner assy because which is making noise and it is noe fix, I went to hear all the other parts like compressor, ps pump ,alternator, water pump using a mechanic stetoscope and not in those parts even on the engine itself.. I need help :)

Re: like hissing noise
 

exhaust leak at the manifold?

Re: like hissing noise
 

Thank you 97emsedan.... and also to the site... my son is using it for school so I will be checking on it sometime, I think he can use it for now after I test test drive.... Thank you so much again .......

Re: like hissing noise
 

could just be the expansion valve doing its job

Re: like hissing noise
 

Thanks for the info Holmesnmanny.... one time after I turn off the engine I heard a hissing sound also so I went under the car, does the expansion valve makes sound after engine off?
here is a recorded sound while I am down under the car and engine is off ...

Re: like hissing noise
 

here is the another recorded sound while engine is running....

Re: like hissing noise
 

Also, 97 Emsedan.... Is it safe to attach a shop vacuum on the tail pipe to locate a leak... my friend told me about that but I am afraid I might mess up the catalytic converter and might suck up oil, I realy have no idea..

Re: like hissing noise
 

the expansion valve acts as a barrier in the ac system to create pressures, when the car is off the pressures start to equalize and that's the sound it appears you are hearing

nothing in the engine is going to be moving when the engine is off so that is likely the sound

does your ac work well ?

Re: like hissing noise
 

Thank you Holmesnmanny..............It seems ac is is working good, I can feel the cold air coming out on the vent and also I remember one time when I was checking all the pulley to find if bearing is bad... I been spinning the compressor pulley to the left and also to the right andthe very first time I spin it I heard like a pressure release sound for a few second but not long on where the line connection on the compressor, do you think I mess up when I spin the compressor pulley maybe on the wrong way? I am very gratefull for your input/help...

Re: like hissing noise
 

Holmesnmanny.... also... when I start my engine my ac is off and the hissing sound is there as soon as the engine runs...then the sounds volume goes low after a while but I think it is still there I recorded it, its the sound on the second video I posted called engine running.....thank you again...

Re: like hissing noise
 

I definitely wouldn't do that. If there is a leak in your exhaust, you will see soot and black areas on the surrounding metal parts where the leak would be. I would check around the exhaust manifold bolts and see if there is evidence of that there.

Re: like hissing noise
 

Thank you so much 97 -emsedan.... I will check and see if there is a sign of those on the exhaust... thank you again...

Re: like hissing noise
 

is it an exhaust rattle ? it's really hard to hear clearly in the video, i can't see where it is that you are recording and you need to record more so it's more clear

Re: like hissing noise
 

Thank you holmesnmanny..... when you say rattling... i think about two object touching or hitiing each other, am I right..... First I am confuse also with the types of sound... the very first time I thought its a bunch of realy tine skinny metal making sounds... then I come up that it sounds like a hiss sound.... I also notice one time that when the ac clcutch engage.. that sounds were almost gone I would think it's gone not unless it is being overpower by the ac compressor working..... and when the ac clutch disengage... then you will here it back....

do you think a starter can make this noise?

Re: like hissing noise
 

i think it's possible it's a bearing that's bad, but the sound you're hearing when the car is off just the expansion valve working

you will need to pull the serpentine belt and spin each pulley and feel for roughness, it could just be one pulley or it could be multiple making noise, since the ac compressor makes it get less sometimes that suggests it's not the ac compressor bearing

normally the first bearing to go is the idler bearing

Re: like hissing noise
 

Thank you holmesnmany... I just change the tensioner assy and my belt is also a month old.....I spin and check all the pulley and it is all good now I remember when I was checking and spinning pulley the very first time, I move to rotate the clutch of the ac compressor before I spin his pulley and I heard a hiss on near the compressor where the two lines were, Is that bad ?

Re: like hissing noise
 

you can add some dye to the system and use a leak detection kit to see where its coming from

Re: like hissing noise
 

Thank you very much for the support and suggestions to you both Holmesnmany and 97 emsedan... you are both a big help to me..... I will be working on the car this weekend when my son drop it off... he is using the car for school.... and he says that it only makes that noise when the engine start running and slowly going away...... good luck to you both and again thank you so much ....