[CL9] Pop sensation/noise when slowing down then speeding up

**peetah** · 26-10-2012 02:30 PM

Recently noticed something odd in my car...

When slowing down for something like a round-a-bout and then taking back off I can feel/hear a slight pop/donk if I step on the accelerator to speed up slightly and then let off it. Doesn't seem to happen if I come to a complete stop or if I power through till the next gear though. Only ever happens in what I think is second gear but could be first. '06 Automatic with almost 85000 km if that helps at all.

My thinking is that it happens if I let off the accelerator at a certain rpm. I notice it from time to time when I'm accelerating up to someone then letting off when I get close enough as well as slowing for traffic at a red light, having it turn green, speeding up to catch up with traffic and letting go.

Had the transmission fluid changed already so really hope that's not it. Based on the fact that it only happens in certain situations as opposed to a certain speed don't think it could be axle related. Getting a feeling it's got something to do with a/f. Feels kind of like it's dumping excess fuel but I don't know if that's something these cars do...

Anyone with any ideas as to the cause? Is it possible that the car is just like that and I never noticed it until now? Going to try disconnecting my battery this weekend and seeing if I still get the same results after a reset.

Apologies if this is covered in another post. Not an easy thing to search up when the issue itself is difficult to describe.

**akina** · 26-10-2012 07:31 PM

Can you feel the pop coming from the front of the car or underneath?

When you say "pop", first thing comes to my mind is back fire from the exhaust. You running any after market exhaust or hi flow cat?

And are you running in "D" or tiptronic?

**peetah** · 26-10-2012 11:37 PM

Regular D mode.

Only mod I've got on is the CT Icebox intake. I THINK it's coming from the front but I could be wrong there. Not a very loud pop/donk/clunk sound but if you're listening for it you can tell it's there. I think I can feel it under my left foot when I drive but could be subconscious. (I rest my foot in front of the dead pedal with my knee bent when I drive)

**aaronng** · 27-10-2012 01:56 AM

Could be either a worn engine mount or suspension bush.

**peetah** · 28-10-2012 05:29 PM

Sounds more like a hollow pop, could it still be mounts or bushings? Need to test more but it could be when the car jerks after letting off the accelerator at a certain speed.

**ryaan** · 28-10-2012 05:52 PM

checked engine mounts?

**peetah** · 28-10-2012 07:44 PM

Would anyone have a link or instructions on how to check? Or is it more a case of something you need to replace to see if it works?

**akina** · 01-11-2012 07:01 PM

look for any cracks on the mounts or around it

**smgl3r** · 01-11-2012 09:33 PM

I have a similar issue. But mine's more like a rumbling noise (as if a rock is rolling in a pipe) following the initial grinding noise. It doesn't happen all the time but usually at low speeds and sometimes when accelerating from a standstill. Weirdly enough it only happens when I accelerate slowly and not when I floor it :S Taking it to the mechanic on Saturday to have it checked. Will post if I find out something useful.

**aaronng** · 02-11-2012 07:22 AM

Revisiting the pop noise, does it seem to sound like a metallic tap noise that happens just once and sounds like it was coming from inside the cabin?

**peetah** · 02-11-2012 09:32 AM

It's extremely hard to describe but IMO sounds more hollow than metallic. I'll try and get a recording but I seriously doubt I'll be able to capture it. Think of a bubble popping but deeper/muffled and louder.

I can definitely feel something when the pop occurs in my left foot. Seems to be when the car "jerks" but only at a certain speed/acceleration combo. Could be me trying to justify the idea that it's an engine mount issue but I don't get the vibration/rattles which supposedly come with blown/worn engine mounts.

FWIW I've disconnected the battery for an hour and reconnected; didn't help.

**aaronng** · 02-11-2012 11:29 AM

Originally Posted by peetah

It's extremely hard to describe but IMO sounds more hollow than metallic. I'll try and get a recording but I seriously doubt I'll be able to capture it. Think of a bubble popping but deeper/muffled and louder.

I can definitely feel something when the pop occurs in my left foot. Seems to be when the car "jerks" but only at a certain speed/acceleration combo. Could be me trying to justify the idea that it's an engine mount issue but I don't get the vibration/rattles which supposedly come with blown/worn engine mounts.

FWIW I've disconnected the battery for an hour and reconnected; didn't help.

If you can feel it by your foot, then I'm inclined to inspect the engine and transmission mounts. The CL9 previously had an issue with a hollow metallic pop sound when going over rough roads or speed bumps. It came from the rear parcel shelf flexing, but you would only hear the sound and never physically felt it.