wierd cooling system problem noise ?

[sweetk30]

so i have the brand new gm L31 engine in my 1987 truck with a edelbrock rpm intake with the 1988-95 style water pump for reverse rotation for serp belt . my heater core feed is intake front right / return rad pass tank top nipple . i have a 195*t-stat with a pin hole drilled in it for burping air as the t-stat with the dingle thingy was 20 bucks more no thanks . rad is a 3 core copper/brass unit for 1981-1991 square body with hd cooling . has a factory shroud on with factory hd fan with thremo clutch that works good .

truck runs 195*-200* all day no problems . tons of winter time heat in the cab no problem . no leaks on the floor from bad heater core .

i was smelling coolant and have checked it 3-4 times no leaks . no loss of coolant . overflow jug is spot on cold line cold and up a inch or so from cold when up to temp.

i notice a growling almost low decibel air horn sound when the t-stat has opened and then i smell coolant . it looks like the system is pushing out the rad cap and in to the overflow tank and sucking it back in . but when i pushes it in the overflow i am getting the hot coolant smell in the cab .

as i said i have not lost any coolant / the rad is to the tip top / overflow working as it should receive and give back .

is there something i missed or did wrong on the system i put together ? or do i just have a super weird weak pressure cap (16psi ) ? or do i need to pull a little coolant from the rad and give a small air bladder of room to keep it from pushing in/out all the time ?

thanks for any help guys have a good day .