"Thunk" sound from back seat area when locking doors

StarmanDXE · Post by **StarmanDXE** » 23 Dec 2008, 07:34

So, I've had the car for almost a week now and I'm still trying to track down this strange "thunk" noise coming from the back seat area. The thing is, it only happens when I lock the doors while the car is moving. But it doesn't matter if I had only unlocked the driver's door or all 4 doors, it will still (potentially) make the sound. (And I don't believe it to be the gas cap door as I have unlocked/locked it numerous times and it isn't the same sound.)

My best guess is that the noise is coming from the rear passenger's side door, but I haven't ridden in the back yet to see if I can be right there when it happens.

Anyone happen to have any clue what could be making this noise?!

Thanks!

StarmanDXE · Post by **StarmanDXE** » 23 Dec 2008, 14:25

Little more info:

The sound only occurs when the car is turned on (and maybe only when it's running?) and seems to happen both upon door lock and unlock (and seemed to be doing it more upon unlock...) Also, adjusting the driver's seat (power) was causing it to make the sound, too... I'm pretty sure the sound it coming from the rear deck (behind the rear seats) and the sound starts off with the "thunk" and then turns into a "whirring" noise (like a spinning motor).

So, anyone happen to know what's back there? Are the seatbelt tensioners motorized at all?

Thanks!

Post by **JRL** » 23 Dec 2008, 17:11

Have you noticed no one has answered you?

Post by **VCA** » 23 Dec 2008, 18:40

StarmanDXE wrote:Little more info:

The sound only occurs when the car is turned on (and maybe only when it's running?) and seems to happen both upon door lock and unlock (and seemed to be doing it more upon unlock...) Also, adjusting the driver's seat (power) was causing it to make the sound, too... I'm pretty sure the sound it coming from the rear deck (behind the rear seats) and the sound starts off with the "thunk" and then turns into a "whirring" noise (like a spinning motor).

So, anyone happen to know what's back there? Are the seatbelt tensioners motorized at all?

Thanks!

I would imagine that you're hearing a lock module that's going south. The lock mechanism has a servo inside that operates an eccentric cam--if you operate one with the door panel off, you can see the external part of the mechanism (white pawl) moving in concert with the sounds--the 'thunk' is normally a 'click' and the retract noise is usually quiet enough that the panel's soundproofing stops it. My RH rear did that (i.e. the 'thunk...whirrr') a month or three before it quit opening on hot days, and then it quit opening at all.

Post by **MadeInJapan** » 23 Dec 2008, 19:38

I was thinking trunk lock....but maybe not. I know that the sound from the trunk is more noticeable than the rear doors.

StarmanDXE · Post by **StarmanDXE** » 23 Dec 2008, 19:59

VCA wrote:I would imagine that you're hearing a lock module that's going south. The lock mechanism has a servo inside that operates an eccentric cam--if you operate one with the door panel off, you can see the external part of the mechanism (white pawl) moving in concert with the sounds--the 'thunk' is normally a 'click' and the retract noise is usually quiet enough that the panel's soundproofing stops it. My RH rear did that (i.e. the 'thunk...whirrr') a month or three before it quit opening on hot days, and then it quit opening at all.

Boy, I hope it's easier to replace the actuator in these cars than it was in my 850. Those locks were broken for 4 years and I just fixed them by replacing all five actuators!

But... I don't ever hear it make the "thunk" noise when the car is off... Leads me to believe that it's not a lock actuator. (And plus, it makes the noise sometimes when I move the driver's power seat and I'm pretty sure it's coming from the rear deck.)

If there's nothing in the rear deck which might make the noise, my next thought was maybe one of the speakers? But that doesn't explain the "whirring" noise...

I suppose I will have to wait until it seems like it wants to do it a lot again and get back in the back seat and try to figure out exactly where it's coming from! (I need to get someone to help me work the locks

)

Thanks for the help!

Post by **VCA** » 24 Dec 2008, 04:57

StarmanDXE wrote:
VCA wrote:I would imagine that you're hearing a lock module that's going south. The lock mechanism has a servo inside that operates an eccentric cam--if you operate one with the door panel off, you can see the external part of the mechanism (white pawl) moving in concert with the sounds--the 'thunk' is normally a 'click' and the retract noise is usually quiet enough that the panel's soundproofing stops it. My RH rear did that (i.e. the 'thunk...whirrr') a month or three before it quit opening on hot days, and then it quit opening at all.
Boy, I hope it's easier to replace the actuator in these cars than it was in my 850. Those locks were broken for 4 years and I just fixed them by replacing all five actuators!

But... I don't ever hear it make the "thunk" noise when the car is off... Leads me to believe that it's not a lock actuator. (And plus, it makes the noise sometimes when I move the driver's power seat and I'm pretty sure it's coming from the rear deck.)

If there's nothing in the rear deck which might make the noise, my next thought was maybe one of the speakers? But that doesn't explain the "whirring" noise...

I suppose I will have to wait until it seems like it wants to do it a lot again and get back in the back seat and try to figure out exactly where it's coming from! (I need to get someone to help me work the locks )

Thanks for the help!

You're going to make me dig out the wiring diagrams, aren't you?

Well, I'll have a look and see what, if anything, central locking and PSML have in common that would be behind you.

StarmanDXE · Post by **StarmanDXE** » 24 Dec 2008, 08:17

VCA wrote:You're going to make me dig out the wiring diagrams, aren't you? Well, I'll have a look and see what, if anything, central locking and PSML have in common that would be behind you.

Appreciate it! Where do you get your diagrams anyway? I'd gladly look at it if I had it... :-/

The only thing I can think of that they would share is maybe the ground?

StarmanDXE · Post by **StarmanDXE** » 29 Dec 2008, 22:15

Well, I think I have figured it out. I believe that the noise was coming from the seatbelt tensioner for the center seat in the back. The long, tube part of the tensioner was touching the metal body part of the rear deck (also the "roof" of the inside of the non-door part of the trunk). I pushed the tensioner up so that it is no longer in contanct and I haven't heard the noise since! I guess the tensioner was moving or doing something and resonating this sound through the body of the car...(?)

StarmanDXE · Post by **StarmanDXE** » 01 Jan 2009, 07:55

Well, it finally started doing it when I had someone else in the car to mash the door lock button for me so that I could locate the source of the noise. The sound is coming from the two rear deck speakers! So, now I have to wonder if just those two are shorted somehow/somewhere, or if all of the speakers are making the noise and those two are just the most noticeable due to their size...