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Old 12-03-2020, 02:44 PM   #1
spock345
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Default Loud rattle/buzz at 65mph Volvo amazon

I have been driving my car on the highway recently and have noticed a rather loud metallic rattle/buzzing noise coming from the back of the car when I hit 65mph. It doesn't seem to be linked to rpm as it occurs only in 4th gear at about 3500rpm. It occurs a bit past that RPM as well.

The sound is a sharp metallic buzzing. It makes me think of two pieces of sheet metal rubbing against one another. Kind of like if you didn't screw down the license plate correctly.

I though it may have been some loose trim but I secured that and it still makes the noise. I've gone over the back of the car making sure anything that could rattle is secured.

I noticed some play in my trunk latch. Although I don't think that should cause such a noise.

Maybe the exhaust? Although I haven't noticed any leaks and it isn't rubbing the undercarriage.

Has anyone encountered a similar noise? Any ideas on what I could check?
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Old 12-04-2020, 02:00 PM   #2
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Maybe the exhaust? Although I haven't noticed any leaks and it isn't rubbing the undercarriage.
That is where I would check. Look close for incipient cracks where the pipes go into the muffler and resonator. Also, parts can come loose inside a muffler. Bang on it with your hand and listen for rattling.
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Old 12-04-2020, 04:06 PM   #3
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That is where I would check. Look close for incipient cracks where the pipes go into the muffler and resonator. Also, parts can come loose inside a muffler. Bang on it with your hand and listen for rattling.
I did notice a leak between the manifold and downpipe today. So there is one. I am thinking the joint at the rear muffer (new simons 2" system) might be leaking. I patched up some leaks elsewhere already.

The rear trunk latch or trunk hinge buzzes or rattles a bit when I hit the bodywork. So maybe that is it.

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Old 12-04-2020, 08:46 PM   #4
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Oh, so you have a new exh system. Well, check your installation? You have likely done that already.

Much more likely for a loud buzz to come from exh because it is bolted to the engine, unlike body parts that are insulated by the mounts.

I once had a loud exh buzz that was very hard to find. Turns out the head pipe was built with two short pipes welded to the flange, into which the main pipes were inserted and fastened. When one of those came unfastened inside the short pipe, it looked normal, but made a lot of noise.

Edit to add: You say it sounds off in 4th gear at certain rpm. Do you hear it at the same rpm in other gears?. If not, I guess I don't suspect the exhaust.

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Old 12-05-2020, 12:41 AM   #5
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Originally Posted by Harry Tuttle View Post
Oh, so you have a new exh system. Well, check your installation? You have likely done that already.

Much more likely for a loud buzz to come from exh because it is bolted to the engine, unlike body parts that are insulated by the mounts.

I once had a loud exh buzz that was very hard to find. Turns out the head pipe was built with two short pipes welded to the flange, into which the main pipes were inserted and fastened. When one of those came unfastened inside the short pipe, it looked normal, but made a lot of noise.

Edit to add: You say it sounds off in 4th gear at certain rpm. Do you hear it at the same rpm in other gears?. If not, I guess I don't suspect the exhaust.
I don't hear it in any other gears. Maybe the load at 65mph in fourth causes just the right combination of vibrations to resonate a bit.

A relative suggest that it may be wheel bearings, but it sounds more like sheet metal than the hum bad wheel bearings make. My wheel bearings in the front are new but the rears haven't been touched yet and are on my list.

I am thinking maybe my trunk latch (old and worn, lots of play) or license plate if it isn't the exhaust.

I replaced the U bolts the exhaust kit had with band clamps. Those sealed up two leaks. I just smeared high temp RTV on the manifold to downpipe joint and put it back together. We'll see how that does when the silicone is done setting.

The odd thing is that there is no hint of the noise until 3500rpm in fourth.
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Old 12-07-2020, 07:41 AM   #6
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The rattle I couldn't find in my amazon was the rear door hitting the wheel tub. I'd double check to make sure your hatch isn't touching somewhere, these cars aren't the stiffest things on the planet, mine gets a resonance occasionally as well.
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Old 12-07-2020, 03:12 PM   #7
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Originally Posted by spock345 View Post
I have been driving my car on the highway recently and have noticed a rather loud metallic rattle/buzzing noise coming from the back of the car when I hit 65mph.
But officer, I have to go faster than 65, my car is not happy at 65.

OK, seriously... do you have speakers in this thing? Attach a waveform generator to create the exact frequency of the trouble, turn up the volume, and if it's a mechanical looseness in the bodywork it will make itself obvious. You can walk around the car, open doors and trunklid, lay hands on panels and trim... waaaaaay easier to find NVH issues at a standstill than at highway speeds.

Not sure how well speakers would excite a muffler rattle, but you could modify the approach.


PS. 3500 at 65?? Holy cats. Install an OD and solve all your issues at once.
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Old 12-07-2020, 04:24 PM   #8
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But officer, I have to go faster than 65, my car is not happy at 65.

OK, seriously... do you have speakers in this thing? Attach a waveform generator to create the exact frequency of the trouble, turn up the volume, and if it's a mechanical looseness in the bodywork it will make itself obvious. You can walk around the car, open doors and trunklid, lay hands on panels and trim... waaaaaay easier to find NVH issues at a standstill than at highway speeds.

Not sure how well speakers would excite a muffler rattle, but you could modify the approach.


PS. 3500 at 65?? Holy cats. Install an OD and solve all your issues at once.
The joys of 4.10 rear gearing an a four speed transmission. I need to find an M41 for this car but I have a few other things to fix first, like the door sag.

I like the speaker idea. Some more incentive to get the radio working. I don't have a waveform generator but could probably just create a bunch of MP3s at different frequencies and fine tune them until I get to the right one. It'll probably confuse and annoy the neighbors at the same time, perfect.
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Old 12-10-2020, 12:34 AM   #9
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from https://www.gocomics.com/closetohome/2015/02/03
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Old 12-10-2020, 04:43 AM   #10
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When you hit 75-80 in 4th the noises get quieter
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Old 06-15-2021, 11:55 AM   #11
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Finally figured out the noise. It was the torsion bars that hold up the trunk lid vibrating against each other and the body.

A few scrap bits of vinyl in the right spots quieted everything.
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