Buzzing inside the frame rail??

[Mucci]

I’ve spent the past month trying to track down a metal buzzing noise coming from the passenger side at 2500rpm. 
 

At first I assumed it was the botched floor repair with hastily tack welded galvanized sheet. So I cut out the floor and replaced it with a fresh panel from restoration designs. Por-15’d everything, used seam sealer and then 3M underside coating. 
 

The buzzing continued. Next I assumed heat shield. I yanked it out. The buzzing continued. I had my girlfriend drive the car at 2500rpm while I sat in the passenger side and can pin point the sound to exactly where the frame rail runs under the floor at the front edge of the foot well. There’s basically nothing around that rail to buzz anymore which leads me to think it’s something inside the frame rail??

 

Has anyone experienced this? I’d love some insight before I go cutting up the floor I just welded in. It’s driving me crazy. 

[Mike G]

Have you looked at where the frame rail meets the firewall from inside the engine bay? Something could be stuck there. Missing 10mm socket perhaps?

[2002iii]

1 hour ago, Mike G said:

Have you looked at where the frame rail meets the firewall from inside the engine bay? Something could be stuck there. Missing 10mm socket perhaps?

I dropped a nut down there the other day and when I used a magnet to retrieve it I also got a hose clamp and a washer.

[NickVyse]

What sort of exhaust do you have?

[2002FjordBaur]

Wasp nest? ?

Edited April 27, 2022 by 2002FjordBaur

['76mintgrün'02]

I found a stubby Snap-on screwdriver on top of my frame rail, as well as the cap to my washer-fluid bottle.  

[TobyB]

I had a PicQuik do a couple of seasons in that location, too.

 

And if something goes down the tube from the front, it'll come to rest inside.

 

t

giant magnet.  No, not to retrieve it, just to stick it in place so it doesn't move.

[JerryC]

I had a '71 1600 that had a frame rail fully packed with acorns after it had sat in a barn for a while. They didn't rattle, but they did accelerate the rusting out of that area.

Maybe there's a broken weld or two that normally fastens the floor pan  to the frame rail. Or, my usual suspect is exhaust. How is the rear transmission mount and the shift linkage? I once had a rattle from "down there" that I didn't pay much attention to until the shift tower came loose from the transmission. The whole shifter moved up and down quite a bit after that, as I recall.

If you get under the car with the engine running, it's a pretty short reach to the throttle linkage and you can rev it to your heart's content. Just make sure it CAN'T ROLL, working e-brake and wheel chocks at least.

 

Jerry

Edited April 27, 2022 by JerryC

[Mucci]

11 hours ago, Mike G said:

Have you looked at where the frame rail meets the firewall from inside the engine bay? Something could be stuck there. Missing 10mm socket perhaps?

 

10 hours ago, 2002iii said:

I dropped a nut down there the other day and when I used a magnet to retrieve it I also got a hose clamp and a washer.

A hose clamp!? I'll have to have another look. I thought the top side of the frame rail at the firewall was capped off. Of course I just covered it all with underbody coating ? I'd be surprised if it's something loose because once the noise started it's been relentlessly consistent.

I'll keep my fingers crossed. Solving this buzzing with a magnet and being rewarded with an artifact would be much preferred to cutting a hole in my new floor. 

The buzzing sounds like thin gauge steel so I'm probably not getting and sockets out of the deal unfortunately. 

 

 

54 minutes ago, JerryC said:

If you get under the car with the engine running, it's a pretty short reach to the throttle linkage and you can rev it to your heart's content. Just make sure it CAN'T ROLL, working e-brake and wheel chocks at least.

 

Jerry

Unfortunately I can't replicate the noise with the car on stands. It also goes away when I'm not sitting in it. I've tried cranking up the idle to 2500 to hold the buzz while I investigate but it's damn elusive outside of on-road driving. My drive up ramps aren't tall enough since the car's lowered but I think I need to figure out way to get the car high enough, on it's tires, with someone in the seat so I can finally have a look from underneath while it's buzzing.

 

 

1 hour ago, TobyB said:

giant magnet.  No, not to retrieve it, just to stick it in place so it doesn't move.

A friend recommended this. I enjoy it's simplicity but I'm terrified that it'll hold off the buzzing just long enough for me to get the new interior fully installed. That's usually how these quick fixes go for me.

"Hey...remember that corner you cut? Here let me remind you..." - every "finished" car project I've had. 

[Mucci]

10 hours ago, NickVyse said:

What sort of exhaust do you have?

Long tube headers to a 3-bolt flange about 8inches after the trans exhaust hanger. It's got about 3" of clearance from the passenger floor so I know it's not rubbing. 

[NickVyse]

30 minutes ago, Mucci said:

Long tube headers to a 3-bolt flange about 8inches after the trans exhaust hanger. It's got about 3" of clearance from the passenger floor so I know it's not rubbing. 

 

Certain there isn't a loose internal baffle if the resonator has been replaced with a box?

[tomphot]

I had a similar buzzing noise in my car that only started at higher rpm's, it was really hard to figure out where it was coming from.  I finally realized that the shift knob wasn't screwed all the down.  Buzzing gone.

[Son of Marty]

I have found a 10MM socket between the tubes on a long branch header that caused the exact symptoms your describing.  

[Leucadian]

Check your rear subframe to body support bracket.  Official part name is a 'push rod', over time those can crack and fail and eventually the bracket contacts the frame rail, causing a buzz.

 

 

ask me how I know.  

[JsnPpp]

All good suggestions. Also, try compressed air from one end and all around to see if anything blows out or shifts or something. On my e30 I had a buzz that I thought was the catalytic converter but was a slightly loose 02 sensor.

 

Passenger side steering linkage pivot?

 

~Jason