My speakers are also vented and I have used software to examine the infrasonic spectrum of a number of music files and to my dismay I have found that in many cases there was substantial infrasonic content present which could cause my amplifier to waste power, or depending on the loudspeaker design, have excessive driver excursion which could result in damage or at the least a waste of power needed for the reproduction loud passages of music without clipping.
My bet is that you have unwanted infrasonic information in the stream or at least musical content below the speaker's low frequency reproduction capability.
I am not sure whether you could filter out the unwanted low frequency noise at your end or not.
The other possibility is that the amp has a stability problem that is manifesting itself as low frequency oscillation which could produce the same effects. If the same chuffing occurs with shorting plugs placed in the input jacks, then there is a stability problem with the amp.
I not sure if some kind of problem in the preamp upstream could also cause this or not.
Be well.
Scotty