TDA2030L Audio distortion at high volume
"Pulses" and large cone displacement suggests the PSU may be shutting down due to too much current demand, then restarting to see if the demand has gone away, shutting down again ad infinitum. 2A isn't very much, with a low impedance speaker.

The large displacement comes from C4 discharging and then re-charging each time this happens.

If this is the case, a voltmeter on the 19V supply will show large fluctuations when the overload occurs.

Either uprate the PSU to about 4A, or try an 8 ohm speaker.