I put a 1/4 spacer under carb now it whistles loud.
Stock 350 chevy in my Elky edelbrock 750. Anyone (heard) of this.

 

is it affecting the performance at all or just making noise? how loud is it?

 

No its not hurting anything .You can here it standing beside the car but not while you are driving.Open spacer i made out of wood.

 

Vacuum leak

It's not covering all the holes properly; either the intake, or the bottom of the carb. Somewhere, vacuum is escaping.

 

Thanks ill check that tonight

 

Just look for the pile of vacuum on top of the intake Don't forget to use the special tool to clean it up, known as a "vacuum cleaner"

 

I had an identical problem.
I looked all over for vac leaks and there were none, it was whistling loud at idle and it would go away by 1/4 throttle.
It ended up that the spacer was misaligned with the throttle bores. The edge of the spacer was protruding slightly into the airflow just below the opening of the throttle blade at idle, creating a perfect whistle.
Another thing that can create a whistle is a PVC port that goes directly into a throttle bore (cheap spacers only)

 

sorry posted two late...