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.