Annoying loud rattle in my 355

There are any number of things in the bay that can rattle:
a) exhaust header heat shield
b) muffler heat shield
c) bypass valve
d) anthing aftermarked pop-rivited in the bay
e) loose exhaust clamp (heck, loose anything)
f) engine (or tranny) mount allows metal to metal contact

Put the car in a safe position, warm, and have someone hold the enigne at the speed where the rattle is evident. Then you get to poke and prod around the bay to see what is causing the noise.

 

I once had a rattle that was louder than the engine at 8500rpm w/tubi exhaust and test pipes. It ended up being a bolt in the exhaust hanger that was loose. I still can believe a single bolt could make such a noise.

 

There is still a lot of stuff you can check (safely) with the engine off, and cool. I would also check the heat shields on the Y pipe, I had an issue with that and had them tack welded down. Not easy since the shield metal is quite thin.

Just look carefully, and check all the exhaust brackets, as it is possible one vibrated loose or is broken. Then muffler clamps are expecially fragile and rattle really bad when broken...of coure Hill Engineering makes suitable replacements that are much stronger.
Tapping gently with a rubber mallet or handle of a screwdriver can help find the resonance that creates the rattle sometimes.

 

A) when you depress the clutch pedal the noise stops? {yes, no}
B) when the gear selector is in neutral the noise stops? {yes, no}

 

Same problem with mine. It is driving me nuts! Only when engine is real hot. It happens when accelerating and decelerating. I found as f355spider suggested, my y-pipe heat shield was loose and rattling. I secured it with a hose clamp so I couldn't move it anymore by hand. Thought for sure that was it. NO! Still something rattling. Being that it happens when it's hot makes me think it has to be a heat shield somewhere because everything expands when it's hot. So something is loosening up. Interested to see what you find. My car is in the shop at Bradan and they guys are tack welding the y-pipe shield. Let see if that is still the culprit.

 

I had one nagging exhaust rattle (also only when hot) that was intermittent for two or three years...it finally started happening often enough I took it to the good folks at Ferrari of Seattle, and they diagnosed a loose baffle inside my factory oem exhaust. They replaced it with a known good, low mileage used one.

 

Anyway to diagnose that with the muffler still in the car? How did they find it was that?

 

That's what mine is. After tapping with a rubber mallet with air boxes off, exhaust heat shield off, sticking a camera inside the Tubi, and grabbing certain pieces to eliminate the sound, it is a loose baffle inside the muffler.
Time for a new muffler!

-Billy

 

I would also check to see if the inside wheel well covers are loose. Mechanics don't always secure them as they should. just stick you hand and tap on them and see if they rattle.

 

I am not positive, I would suspect they had a couple guys working on it and listened for the noise with the engine lid up? I am pretty certain they did not take the muffler off to diagnose the problem.

 

I'd check the airboxes to make sure that they are secure. The rubber mounts they are on have a habit of ripping apart, and the airboxes can rattle when the car is accelerating. That is what happened to me.

 

Not the air boxes on mine either. Can't wait til you find out. I'm betting it's the y-pipe heat shield as I think mine is. Not sure even a spot weld will stop the rattling.

 

I had a bad rattle in my muffler from my OE cats going bad sending parts into the muffler years ago.

The sound went away with high flow cats from Mr. Helms and the junk finally shot out of the muffler after a year or so or just finally broke apart enough.....

 

Put your ear by to the gear box when engine is running, I bet the clutch disk is making the noise.

 

I get a rattle when the car runs hot too. In my case it is caused by the exhaust bypass valve vibrating. Should cause no issues aside from the noise

 

If it is the bypass valve, wouldn't it rattle at idle too? My rattle is only when real hot and under load. Can't get it to rattle when just revving it in my garage when I come back from a cruise. This is why it's so hard for me to find.