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Discussion Starter · #1 ·
I'm not really sure how to describe this, but my car has been doing this since day one. I don't know if this plays into it at all but I have a manual transmission. Sometimes (not every time) I start the car and let it idle, about 10-30 seconds after the vehicle is started it makes a thunk noise. It is not extremely loud, but it is noticeable. It almost sounds like something is engaging. If my foot is on the brake pedal or the floorboard I can actually feel a small 'bump' at the same time I hear this noise. I asked the Ford dealership what it was and they told me that it was the A/C compressor engaging. They said that even if you don't turn it on it will come on every so often so the compressor doesn't freeze up. I am not 100% convinced that this is the problem. Has anyone else encountered this or know what it is?
 

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It sounds like the A/C to me. Since it robs a bit of power when it is on, I can see how you can feel it.
 

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I know with my 97 ranger with auto it does that some times and I found out it was the spyder gears in the rear has a little more play and it would let the gears move a little when appling power forward or reverse. It may not be that.
 

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Discussion Starter · #5 ·
It makes this sound before you start moving?
Yes, and it doesn't matter if the car is in neutral or if it is in gear with the clutch engaged. It may very well be the A/C. Have any of you ever heard this in your own Mustang?

I know with my 97 ranger with auto it does that some times and I found out it was the spyder gears in the rear has a little more play and it would let the gears move a little when appling power forward or reverse. It may not be that.
I think I know what your talking about and when I actually start moving sometimes I can hear the gears engaging in the rear end. The sound I am hearing seems to be coming from the engine compartment though...
 

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Yes, and it doesn't matter if the car is in neutral or if it is in gear with the clutch engaged. It may very well be the A/C. Have any of you ever heard this in your own Mustang?



I think I know what your talking about and when I actually start moving sometimes I can hear the gears engaging in the rear end. The sound I am hearing seems to be coming from the engine compartment though...
I believe I get the same sound as you doubledco.... i believe its a non-issue.
 

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I had never noticed this noise until after reading this thread. I've only had my 05 GT since December so I haven't used the air that much. Then last night I had the A/C on after stopping to eat. A short time after starting the car I heard the thump. It is kind of a disconcerting thump but I'm assuming that it is just the compressor kicking on since I had the A/C on... and I usually don't... and I had just read this thread about 3 hours earlier.
 

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Front end there is a lot of things to check. I would also look at the motor mounts. They may have lost there liquid
 

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My car and a few others from these sites have this going on.With mine, every so often while I'm waiting for my wideband to cycle down on the drivers sides it sounds like someone has hit the floor board under my seat with a 2 x 4.Scares the living daylights out of me and my passenger.I have been told it might be exhaust expansion.There are threads out there on this subject if you search for them.I haven't heard about any negative effects from this.
 

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One surefire way to determine if the A/C compressor is engaging is to open the hood and watch it while someone else starts the engine. It normally makes a clicking noise when it engages.
 

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One surefire way to determine if the A/C compressor is engaging is to open the hood and watch it while someone else starts the engine. It normally makes a clicking noise when it engages.
You could also remove the belt and listen:scratchchin
 

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Discussion Starter · #12 ·
Yeah, I'll take a look at it this weekend and post back what I find out.
 
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