AHC noise? Should there be one?

[Wah00]

2006 LC with AHC. Since swapping to much quieter tires from mudders, I now notice an occasional buzzing sort of noise while driving. It is faint and feels like it is underneath me. Sounds a little like a pump or power drill running in a quick burst or two. Not acceleration or brake related. I’m thinking it would make sense if it is the AHC adjusting itself. Should that be silent, if so? Is that a bad assumption? Do I need a tech stream for this? So many questions. . .

 

[MycoManiac]

It’s probably the brake. It cycles on and off and it’s not actually in sync with braking. I guess you could hear the AHC pump, but what you’re describing sounds like brake booster.

 

[Wah00]

Thanks. Braking seems fine - is the booster a wear item that I should replace at this point given the fact that it’s making noise?

 

[MycoManiac]

Thanks. Braking seems fine - is the booster a wear item that I should replace at this point given the fact that it’s making noise?

I mean the brake assembly can be a big point of maintenance. But if you’re not getting lights and buzzer, and you do regular maintenance on the brakes, that sound is completely normal.

You can test the assembly booster with a short procedure, to make sure your brakes are functioning within spec. But that doesn’t test everything.


The sound is normal, and yes it can be heard and felt. I also wondered this for a while. But you should be fine. Go ahead and do PM on it though, never hurts and probably could use it.

 

[Wah00]

So .... I had it in for some maintenance and had them check out the noise. They diagnosed "left exhaust manifold" needing to be replaced. That doesnt seem to me like it could be the source for the noise I was hearing - which sounds like something adjusting back and forth mechanically (like an AHC or brake booster).

But, as I have admitted before, I'm not even a shadetree mechanic, so my opinion is pretty worthless. Do you think the left exhaust manifold could make noises like that?

 

[MycoManiac]

So .... I had it in for some maintenance and had them check out the noise. They diagnosed "left exhaust manifold" needing to be replaced. That doesnt seem to me like it could be the source for the noise I was hearing - which sounds like something adjusting back and forth mechanically (like an AHC or brake booster).

But, as I have admitted before, I'm not even a shadetree mechanic, so my opinion is pretty worthless. Do you think the left exhaust manifold could make noises like that?

what about the manifold?

They can crack, but it sounds like a cracked exhaust manifold. Ticking sound that will usually go away as it warms up.

It honestly sounds like your brake assembly. You can hear it. At least I have been able to in both of the 100s.

 

[Coin]

When the AHC adjusts itself you will feel the car front or rear move up or down. It does do this occasionally at stop lights etc. If driving it's most likely the brake booster.

 

[Wah00]

agree with these comments. brake booster makes a lot more sense to me.

 

[FJC]

FWIW - I have a 06 LC with AHC and when its automatically adjusting heights due to weight or whatever there is a slight buzz heard. It adjusts while driving also, especially if passengers in the back or added weight after loading up stuff.