My car engine sounds like BB's in a coffee can !

My bone stock 1966 C Code on light acceleration/deceleration 1200-1800RPM range makes a sound like BB's or samll nails in a tumbler from engine/exhaust header area. Background: I removed smog pump a year ago and didnot have the noise. It is timmed to 10 Deg. Int. Total is 32 @ 2500RPM. Vac. Adv. 15 deg. in at 1200. Carb set correct (float level etc.) Plugs reflect good burn. Vac. @ 17". I'm wondering if the extra o2 from smog pump was burning any extra fuel that carried over to exhaust? Live in So. Cal. (Thermactor still on) was on when I bought in 2010,so only removed pump to date. It's not like a backfire but a rattle or small fire crackers. Below and above above RPM range no problem? Any help appreciated as I'm out of ideas. Thanks in Advance.
 
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After I had to buy a replacement pump once when mine wore out, I started leaving the belt off except when I took it in to smog. When it finally got old enough so I didn't need to smog it, I took the pump off and put plugs in the end of any open hoses. I never had any issues with noise or pinging. Not sure what is causing your problem, but based on my experience, it isn't the missing smog pump.
 
After I had to buy a replacement pump once when mine wore out, I started leaving the belt off except when I took it in to smog. When it finally got old enough so I didn't need to smog it, I took the pump off and put plugs in the end of any open hoses. I never had any issues with noise or pinging. Not sure what is causing your problem, but based on my experience, it isn't the missing smog pump.
Thanks Hwyman--Maybe it's not related but need to remove Thermactor headers and plug the heads like you. With Thermactor manifolds on the spark plugs are a PITA to change .
 
What fuel are you using? What you describe sounds like it could be predetonation, which can destroy pistons and bearings. If you are using premium fuel (92-93 octane) a stock 289 should be fine. If you are using CheapoEthonol 87 octane then this may be your problem. These cars were built when we had leaded gas at 100+ octane. I have in the past described the sound as someone crinkling up aluminium foil or hard celophane plastic under the hood. It tipically happens only when the engine is under a load such as initial take off from a stop or climbing a hill. Exsessive carbon build up in the combustion chamber and top of pistons can cause predetonation as well. So, if your wondering why you never had the problem before, this is a possability.
 
What fuel are you using? What you describe sounds like it could be predetonation, which can destroy pistons and bearings. If you are using premium fuel (92-93 octane) a stock 289 should be fine. If you are using CheapoEthonol 87 octane then this may be your problem. These cars were built when we had leaded gas at 100+ octane. I have in the past described the sound as someone crinkling up aluminium foil or hard celophane plastic under the hood. It tipically happens only when the engine is under a load such as initial take off from a stop or climbing a hill. Exsessive carbon build up in the combustion chamber and top of pistons can cause predetonation as well. So, if your wondering why you never had the problem before, this is a possability.
I here you with the fuel,previos owner used 89 grade I use 91 octane. I grew up in the sixties so I know this calif. gas is crap now! When egine gets up to temp.,sound is less pronounced. I'ts diffently in the engine I disconnected Vac. Adv. but still does it,thougt it might be advancing to quick. When decelerating I can have my foot off the gas and it still makes sound around 1500 RPM's. This is where my vacuum adv. was all in so tried the above disconnect. Need to get audio file. Thanks all for your help ,will get back with more info. once it stops raining.
 
Have you checked or tighten the header bolts? If this noise gets better as the engine is warm.. i would check for exhaust leaks at the header. I had a header leak that was so bad it sounded like my engine was about to come apart ..turns out i blew one of the header gaskets.
 
If you still have the Thermactor tubes on and the hoses aren't plugged you'll get that sound from the anti-backfire valves.
bartl-Thanks for info ,yes I stll have thermactor manifolds on and check valves.Check valves now have a rubber cap and hose clamp where hose would have went. I guess if valve malfunctioned it makes sense. Need to remove one day but they are a PITA so waiting for engine rebuild. Again thanks to all for the help.