328 mystery rattle

The 328 was just serviced It came back with a rattle that only appears between 3500 and 4000 rpm. I thought it was the mesh screen on the bonnet. I was not. The sound is coming from the passenger side rear. The sound is one of one thing vibrating against another. Has anyone come across anything similar. These things drive me nuts.

 

Check the duct from the body side scoop to the air filter housing. I had a buzz/rattle one time at certain RPM's and found the duct contacting the car body. A little foam tape took care of it.

HTH,
Dave

 

happened on my previous 308. Check the exhaust system carefully. On the passenger side, the rear bank header snakes over the frame and can touch there. Especially under accelleration (in my case). I little careful bending of the heat sheild around the header tube improved the clearance to eliminate the noise.

 

Theo,

I have a similar low speed rattle/squeak from the passneger side rear. I have been through a number of things;
1. The air cleaner may contact some A/C pipes
2. The heat shields on the exhaust pipes are loose...is that normal?

I still can not isolate the source. If you have any luck let us know.

Bill

 

I will probably take it to a body shop nearby. I blew the better part of today searching for the cause. The exhaust was not touched. My guess is that I can rule that out. I will check the intake scoop. That is a possibility.

 

Dave Handa's suggestion is a good one ( I have this too) but more likely it is the AC lines vibrating against the inner rear fender. You can access this by removing the passenger rear wheel and plastic wheel well. You'll see two (?) black tubes near the air intake tube. Place padding between the body and the AC lines. This was an extremely annoying rattle for me and I am glad its gone !

 

Thanks all,
Maybe I will tackle this one a bit more. The AC lines air intake sound like possibilities.
The rattle is constant at 3500 to 4000rpm. No problem below or above 3500 to 4000.

 

While you're at it, check the large coolant line the comes down from above the WP, & bends diagonally across the engine & in front of the alternator.

It needs to be exactly centered between the gas tank & the alternator pulley. Otherwise it'll rattle at some speed & wear a hole in itself or the gas tank.

Usually they have a rubber sleeve over them to help deal with this problem, but a lot of the sleeves have gone walkabout over the years.

 

Oh, yes,
forgot the old 'loose fuel tank strap' rattle. Very speed sensitive (which this one is). The strap only vibrates when something excites it near it's mechanical resonant frequency.

Fix is to put a strip of rubber like material under the strap & snug the strap down.

If the fuel tank was pulled for the service, this may be your culprit.

 

Checked the fuel lines, water pipe going to the front and air intake. The rattle is there to drive me nuts. I padded everything. Any other thoughts? How about the mesh screen on the bonnet? Is it possible?

 

I use to have the exact same rattle noise. It turned to be a metal shield protecting the accesory belts.

It was a little bit bend, probably because a previous owner tensioned the alternator belt without removing it. Was bend enough that when the engine was in the 3500 to 4000 rpm it was rattling against the exhaust.

- Julio.

 

Must be a built in resonance, perhaps in the motor, at 3500-4000 rpm. Rattles and buzzes there are a VERY common complaint. I've got a 'buzz', I'm going with the theory that it's A/C hoses.

 

I had the same noise at 4000RPM and it was the hard A/C lines next to the firewall. I used some foam rubber between the lines and the vibration was gone.

 

I got it! Last evening the car began to make racket at idle. The sound was similar to the mechanical noises of an engine going south. I was freaking all the way out. The car has been relatively trouble free for several years. I had a guy come out from a local independent shop last evening. He pulled the fender well and discovered the water pump dancing up a storm. They removed, rebuilt and reinstalled the pump today. I drove the car a little bit ago. The buzz is gone. Somehow the weakening water pump was the culprit. I don't get the association. However, all is well again.