weird noise

[Handy Andy]

Ok gents, My newly rebuilt 400 small block is making a bit of a weird noise, I think.... when driving down the road, if I give it a little bit of gas I get this tinny rattling noise that sounds like it's coming from the exhaust behind the cab. But it only sounds like it is doing it on the drivers side of the truck. The exhaust consists of flowtech afterburner headers, 2.5" from the collector flange into a set of super 10's and then 2.5" back that dump out right behind the wheels.

I've verified that the exhaust pips are in fact not banging against anyting. I don't remember what my advance is set to, When i get the truck back from the transmission shop I will verify.

When I rebuilt the motor I put on a set of Dart SHP heads and should have a compression ratio around 9.7:1. It makes this same noise whether i run 87 or 91 gas. I even tried to add some octane boost to a tank of 91 to see if it helps with zero change. Part of me wants to think it is the Super 10 muffler as I have heard that the internals will sometimes rattle. I do plan on switching them out for some hushpower hP-2 mufflers before too long.

Once I get the truck back I plan to pull the plugs and see how they look. I've only put about 850 miles on the truck since the new motor and trans was installed and I'm thinking maybe I might have too hot of a plug in. The other thing I plan to do is pull the vacuum advance hose and plug the port on the carb and then go for a test drive to see if this fixes my issue.

I should also add, if I'm in park and rev the motor it does not make this noise. If i really get on it, as far as I can tell, it does not make the noise. It only does it at part throttle while I'm rolling down the road. I can even sit and power brake and it won't make the noise.

Any other ideas? how bout experience with the super 10's and rattling?

 

[Rusty Nail]

Seems reasonable to me.

 

[HotRodPC]

Check all your exhaust hangers real good and make sure they're tight. Make sure your muffler, pipes and hangers are not to close to the frame and rattling up against the frame. How new are these mufflers? Sometimes they rattle when new until broke in and flash and such from welding and manufacturing is blown out of them.

 

[Handy Andy]

The entire exhaust is pretty much brand new.. less than 1000 Miles on it. I've verified that there is plenty of clearance between the exhaust and anything it could possibly be bouncing up against. The part that really gets me is that the noise sounds like it's coming from the middle/back of the truck, not the engine bay..

 

[78C10BigTen]

I had super 10s and never experienced any rattles. As a matter of fact none of my flowmasters have rattled. Flowmasters are all i use.

 

[78C10BigTen]

Are you sure its exhaust? Maybe its something behind the seat or in the bed that makes noise with the mid range vibrations. Sounds stupid but alot off odd noises come from stupid things.

 

[gpmorgan]

I have a set of Flowmaster 40 series and one of them has developed a rattle. You can bump the pipe with your hand and hear it. It rattles when coming to a stop and sometimes when idling. Drives me nuts. Probably time for something else. They are about 8yrs old. Try bumping the pipe with your hand.

 

[shiftpro]

Could be a U joint starting to go. They make all kinds of stupid sounds when they start to stick. Clicking , chirping, intermittent drive line vibration.

 

[HotRodPC]

Even a good product can have a defect. All it would take is a missed weld or a bad weld come loose and have a rattle in a Flowmaster. Here is a cutaway pic. Just one of them flanges rattling around in the muffler would make rattling noise.

You must be registered for see images attach

 

[Handy Andy]

thanks for the ideas guys. I honestly am pretty sure it's something in the muffler, but i'm going to check all that other stuff i mentioned before and if none of that yields any results then I will go ahead and swap out my mufflers.

I'm fairly certain it's not u-joints because when I did my engine swap I went through them and they were in great shape.

On another note, I completely emptied everything from behind the seat a couple weeks ago so now they only thing back there is the subs that I haven't hooked up yet. There is some stuff in the box that could possible be causing my issues. Guess I'll have to clean it out and try it.

 

[75gmck25]

It definitely could be predetonation/pinging from too much vacuum advance during light acceleration. Some of the stock vacuum advance cans have as much as 20 degrees advance, which might be too much if you are running more static timing.

Disconnect the vacuum line from the distributor and plug it. Then try the same part throttle acceleration. If the sound stays, it was not pinging.

Bruce

 

[Rusty Nail]

I vote for some stuff trapped in the Flows like a piece of honeycomb or something.

 

[Honky Kong jr]

Are you sure its exhaust? Maybe its something behind the seat or in the bed that makes noise with the mid range vibrations. Sounds stupid but alot off odd noises come from stupid things.

To easy..........

 

[78C10BigTen]

To easy..........

Lol ass. Well i find from experience its usually stupid **** like that.

 

[rt66paul]

Yep, like the friend that put marbles in your hubcaps....