Woofers pumping

B&w woofers on my 801's had a condition called Oil Canning.

Was the excursions more evident on one recording over another?

@erik_squires It's only happened twice. With two different amplifiers. Both times the right channel only. The left channel the woofers were not pumping. Already thought of swapping channels but haven't taken the time to do it.

@hiend2 That's interesting. I have never heard of "oil canning". The speakers are B&W 803 D3. The excursions were only evident on two songs, played at levels around 90 dB, from the right channel only,  over a period of the past year.

Never play those two songs again.

OP:  You may have something going on upstream.  Tube pre?

If the pumping you describe was slow, and it’s a tube preamp you may have a leaky coupling cap. Needs to be replaced. More dangerous with DC coupled amps.

If the woofer pops in or out and slowly returns to a center position, it's likely another cap in the circuit. The coupling cap eventually charges to DC and blocks it.