Worn out bushing or steering joint probably.
One clunk when accelerating (but now repeated clunks) and another when braking can be caused by broken motor mounts.
Braking
The braking system makes a car stop.
If it is when you brake then there could be some loose hardware, if so tighten all the bolts that you can and if not when braking then it may be a ball joint.
I think Knock on the door makes more sense. Knock at the door.... What do you knock on at the door? the wall?
Possibly a worn out universal joint.
A bicycle has two contact points with the ground, front and rear wheel. Whatever makes sense to do at one of them (braking or suspension), will probably be sensible to do at the other as well.
check engine mounts
Possibly weak u-joints or transmission mounts
The smaller shoe should go on the front. The larger shoe should go to the rear, but not because of why you might think! When the brakes are applied the front shoe tries to jam itself into the brake drum. It is that front cohesive part that has the strongest braking force - pressing most-so upon the forward-facing shoe. However, even though the front shoe is where the majority of braking force is applied, it does not get the larger shoe! As noted, in a braking mode, the majority of the force that the decelerating vehicle applies to the brake shoes is applied against the forward shoe by the forward-most area of the inner brake drum, this makes the forward shoe the stronger, braking-wise. To help even things out, the rear secondary shoe is designed to be larger, to more equally match the braking power of the smaller, but more powerful front primary shoe. Ergo: The proper place for the larger shoe is to the rear.
change brakes or check drums
Most likely a CV joint...could be dangerous... consult a mechanic asap