Booming sound in cabin

[mojobaby]

Ever since I replaced my engine mounts, I've had a loud booming sound in the cabin. It's worse when the engine idles.

The vibrations are so bad that my rear view mirror vibrates and the parcel shelf rattles.

About the same time as the engine mounts, I replaced my exhaust and also took my carburetor apart for a clean. I thought it also might be my vacuum advance unit, but that has been replaced with a new one and still the booming continues.

If I stand next to the engine while its running, it's relatively quiet, but when I put my head inside the car, the booming sound is ridiculous!

So now I'm think that perhaps those after market engine mounts weren't so great. When I bought them I did notice that they were a lot harder than the existing mounts. Almost like plastic as opposed to rubber.

Has anyone else had this problem? I don't really want to take my whole engine out again

 

[reidalpine]

must be the wacuum advance...As if wacuum No noise -Sorry couldn't resist.
-I'd go over the engine-mounts.for starters slack them off a bit..squirt a bit of oily stuff between mounts/engine-mounts/frame
Then I'd go over the exhaust,
first make Sure the pipe isn't hitting the hole through to fender.then make sure the pipe are not touching Anywhere along to outlet..
slacken off the joints as one could be in a jam.it needs to sit "loose" at all joints.Does it move freely No binding or stuck-feeling??
It must hang freely.. again squirt some lubricant between all rubber/metal to free up

Could be direct or resonant noise,so best check for direct noise first ie all free to move a bit/dangling and not banging into something..

If no use,crank up that stereo I've found Captain Beefhearts Bat chain puller to work wonders -Reid.

 

[Paul Narramore]

"Slacken off those joints as one could be in a jam?" What flavour jam would that be?

 

[reidalpine]

whatever your flavour Paul.. -Reid.

 

[mojobaby]

Could be the rock band, Pearl Jam, because thats what it sounds like inside the car

Thanks for the tips Reid, I'll give them a try once the temperature rises above 3 degrees. i've just remembered that I also added a new "hanging exhaust mount ", if thats the correct term. It was a little difficult to fit as the exhaust has a "kink" in it and doesn't line up too well.

I think all my exhaust hanging mounts are probably too tight, hopefully its just that!

 

[Niels Svane]

Try to press your left foot down in the floor to the left of the clutch pedal. If the sound changes it might be related to the exhaust pipe running beneath the floor at that point. In my car a booming sound begins when I put pressure on the floor at that point.

When my exhaust pipe (where it goes trough the fender) was loose it didnt boom, but rather knocked.

 

[Niels Svane]

Oh didnt think about the vibrations...Those cant be due to the exhaust alone I think. Then your probably right with the mounts or ignition timing.

 

[mojobaby]

Yes thanks Niels, the exhaust is clear of the hole in the inner wing and also beneath the pedals. There's no knocking sound at all, just the loud humming/booming.

I have a sound meter on my iPhone so might give that a test tomorrow-will be interesting to see how loud it actually is.

 

[Simon P]

I have had this noise before on one of my customer projects.
You need to look down the back of the engine to see if the engine timing cover is touching the lower lip on the bulkhead where it meets the chassis.
The one i had i jacked up the engine and made spacers for the engine mountings to lift the engine slightly.

 

[JonathanT]

I remember you telling me that Simon...

Mojo another tack entirely if you have the time . I put 15mm foam between the plastic roof lining and the roof and also vinyl flooring sheet cut into strips into the long troughs on the roof on the underside. The car is very much quieter as a result without the booming element. The doors can now be closed without deafening the occupants too

 

[mojobaby]

Simon P, thanks a lot, it's the first thing that I looked at this morning; it made perfect sense. However, that wasn't the problem as I was able to pull a 10mm rope around the back of the engine and it passed through easily.

I like the "sound" of that Johnathan. It's something I'll probably try. I would never have thought that the roof should be insulated, I probably would have put it in the door panels. Have you done that as well?

However, my problem has been solved (after many months!) Thank you Reid

At the same time that I put on a new silencer, I also ordered some exhaust hangers. The one beneath the back passenger left hand side door was the problem.
The holes never lined up and it was probably the wrong size as there was a gap above the bracket, as you can see in the photo. However, I made it fit, causing undue tension on the exhaust.

So thanks everyone for your tips and advice-much appreciated!

I mentioned that I had downloaded a sound meter app to my iPhone. It's really a great toy to have.

It's a pity that I didn't take the reading before I repaired the exhaust fitting.

This reading is taken standing over a running engine with the bonnet open


And this photo is taken inside the car with doors and windows closed and engine running (still with bonnet open)

 

[reidalpine]

glad to see you sorted it out mojobaby Very annoying problem-It's like opening the rear-windows in a Volvo while moving
sounds like a Harrier jet on take off.. -Reid.

 

[JonathanT]

That's a useful app there Mojo.

Re the roof just tap on it and I guarantee it will sound like a tin drum. Tap on mine and it now gives a short thud - huge difference to the overall sound in the car.
I've not done the doors yet. That's on the cards as I have bought high density blue foam camping mats to cut up for the purpose. Way cheaper than the same stuff sold to car boutique shops. I have also insulated under the rubber mats in the same way.

 

[mojobaby]

Thanks Jonathan, I'll more than likely do my doors sometime this summer. By the way, I know what you mean by the "drum" sound on the roof. Looks like a bit of a mission to take the lining off though!

The booming sound was very much improved after I loosened the exhaust hangers, but I must admit, I wasn't 100% satisfied.

Luckily, I still had my old silencer (with a patched hole), so I put it back on the car today and the difference was immediate. So I think that was the problem all along.
Tomorrow, I'll do another test with my sound meter; it'll be interesting to see the results.

In the meantime, here's a photo of the 2 silencers side by side. The top one is the original and you can see that it's a lot shorter. I've no idea why the longer one gives the booming noise. Maybe it's just a bigger "drum"

 

[JonathanT]

Ooer! Good you have identified the source. The longer one is probably resonant at a particular frequency casing that booming noise

 

[Paul Narramore]

Jonathan, So how easy is it to remove the headlining then? Just lever it off with a screwdriver?

I noticed today just how much slime and even bits of moss were appearing in the passenger window sliders. I've just cleaned them out with a rag for now but how easy are they to remove?

 

[JonathanT]

Jonathan, So how easy is it to remove the headlining then? Just lever it off with a screwdriver?

I noticed today just how much slime and even bits of moss were appearing in the passenger window sliders. I've just cleaned them out with a rag for now but how easy are they to remove?

Headlining isn't that easy to remove or replace frankly. On a GTL its one big plastic thing held on with matching plastic plugs. Choose a warm day. Plastic will be more bendy and less prone to crack. Or use a wallpaper steamer . The side windows all come out pretty easy in their plastic frames can't remember without looking how they are held in. It's then possible to pull the furry stuff out and give it a good scrub with bleach solution. If you have rust corresponding with the drip slots now is the time to deal with that too