Rattle Snake Sound from Rear Exterior of Car

[RyanBorck]

I have an 81 FI Spider.

It happens mainly on deceleration but honestly, very random. I will get this rattle shimmy sound almost like a rattle-snake. I originally thought it had to do with my exhaust system, and still may.

Definitely coming from behind me as I am driving and from the undercarriage somewhere.

I should try to record the sound and post here.

Any thoughts?

[ga.spyder]

Hey Ryan,that could be a lot of things.You automatically think loose exhaust connection.I recently have had a rattling noise from the pass. rear.I found a bushing coming apart on a trailing arm,which I would think is pretty unusual.You did look under the back seat to make sure there isnt a snake in there? Good luck
Craig

[jwhite]

You explained that just like I would of, even the deceleration....well, actually my would make the noise when I would shift gears. As soon as I pushed the clutch in there it was. Mine was one of the mounting points for the moulding that goes all the way around the back of the car above the rear seat. That moulding you have to remove to get the conv. top off. The mounting point is just a thin piece of metal spot welded and it came loose. Funny think is....when it would rattle it made the noise sound like it was coming from the undercarriage, thought it was the exhaust system also. Check it out.....who knows.

[RyanBorck]

Thanks everyone, at least a good start to a few possibilities.

[BurbankJalopy]

I'm nearly willing to bet money on the problem. I have the same car, and I think it's your exhaust rubbing the underside of the car. Mine rubs directly above the rear axle where it arches up to clear the differential. I sort of fixed it by hose clamping a piece of radiator hose around the exhaust so it's metal on rubber instead. You can probably just grab the tailpipe and wiggle around and listen for clanking or scraping on the body. If you still can't verify, you could always jam a piece of rubber or something where it looks like it may be rubbing, and drive it afterward. If it's not the exhaust rubbing, maybe the catylitic converter is melted inside, which would sound like a rattle snake. You can bounce or punch the cat convtr to see if you hear any loose stuff in it. The other possibility is the brake pad spring clips. The pads have springs/clips that keep them from rattling back and forth constantly in the caliper. My car was missing some of these so the pads slip back and forth as you drive,and cause a sound like a rock is tumbling around inside the wheel. If it's these springs, the rattle should go away when you step on the brakes and the pads are then under tension. I also had to replace both trailing arms as they were cracked. Those didn't cause a rattle but more of a heavy clunking.

[RyanBorck]

How much you willing to wager? Just kidding. Actually I really think you may be on to something. The noise does go away when I apply the brakes just slightly. Do I need a brake job to find the issue or is it something I can look at from underneath the car? The rubber buffer idea may also prove valuable as I think there is some rubbing going on down there, too as you described.

Thanks everyone.

[BurbankJalopy]

It would be best to take off a wheel and look at the pads for sloppy fit in the calipers, but you could also park on a level surface and apply the parking brake very lightly, just enough to drag the brakes. Then rock the car back and forth to see if you hear any sounds from the brake calipers as the wheels try to rotate back and forth. Also, I am not recommending it, but a person could very slowly and gently pull the parking brake as they drive and the noise should go away if it is the spring clips missing, as that isolates mostly the brake system as the cause. If it is the spring clips, they are only a few dollars but finding them in the first place for sale is tough.

[RyanBorck]

Okay, well - try to figure this out. I have narrowed down to the exact moment when this sound occurs - at exactly 2500 RPMs. Doesn't matter what gear I am in but once that needle hits 2500 (on the way up or down), the car produces a shutter/snake-like sound.

[ga.spyder]

Ryan,when I got my car it was doing the same thing.I couldnt duplicate it unless I was moving(under load).I put another clamp behind the cat and it went away,so it was something in my exhaust.Little rattles and such drive me crazy.
Craig

[RyanBorck]

I am able to replicate the sound with the car in neutral and revving the engine to 2500 RPM. Had a friend lay under the car in the back, he put his foot up the muffler in the rear and was able to change the rattle. And when you kick the rear muffler, you can hear something clinging around. So I figure, lets just replace the muffler. Now, when I look at the options, I see REAR, CENTER and FRONT mufflers. Are there really three mufflers on this thing? I am leaning towards just replacing the rear portion right now.

[ga.spyder]

Yep,they had 3 mufflers.Mine had the center already removed.I have removed the front(cat) myself.Now I have just the rear Ansa,and it sounds great!
Craig