bizzare clicking / snapping sound in cooling system

Hey there... Got a weird sound coming from the front of the motor, near the thermostat housing. It's a clicking or snapping sound. Almost sounds like an elastic band snapping against paper or something like that. There's no pettern to the timing of the noise either. When you put your hand on the upper rad hose, you can feel pulses with the clicking. It only happens when the car is warm. There's also no heatercore in the car. It has an electric waterpump but this was happening with the mechanical pump as well.

I've tried all different temps of t'stats, both with and without burpholes. The only way the sound goes away is if I don't run a t'stat at all and just use a restrictor. Problem with that is the car only runs at about 150*.

Any ideas or thoughts would be appreciated. It's really annoying!!! Tks.

Thanks for the reply, Walz... It's definitely not the timing chain and the sound only starts once the car is completely warmed up. No air bubbles present as the system has been 'burped'.

I'm lost. Have no idea where to go from here and it's really annoying!

Got it diagnosed as the thermostat snapping open and closed. Apparently the water may be boiling in the block and causing problems. The rad is very warm on passenger side but cool on the drivers side.

Any ideas why coolant would be boiling in the block? The pump is pumping adequately (sound happened with mech pump, too) and the rad is a large, 2 core aluminum. The 180* thermostat is installed correctly.