Why are my woofers pumping?

My former Atlas, made in 2013, was used successfully over a period of several years, before it broke down, after five years - the needle saying goodbye to the cantilever, for unknown reasons. No mishandling on my side. Although the leaning of the LPs was so-so. My first cartridge became non-optimal, after long use ca 1000 hours, and it remains to be seen if the new Atlas extends the score.  

Good luck o-holter. I do have a soft spot for that cartridge. It is totally unbeatable for things like string quartets and not bad at all for rock.

Thanks mijostyn. I like it with all kinds of music. The effect is  that I enjoy listening more. I wonder if it actually sounds slightly better than my former Atlas did when new. Possibly the low output version (Atlas SL) is even better, but I can't risk it with the Aesthetix Io phono stage, which likes the 0.56v output of the standard Atlas. 0.25 or thereabouts may be too little for the Aesthetix to sound its "robust" self. At least if using NOS tubes, like I prefer, even if I get a little more background tube noise. Lyra warns that the SL version is not for everyone, the phono stage must be up to it, or you should use a stepup. However, Aesthetix says no to using the Io with a stepup device, don't do it. I think this would destroy the purity of the design and be a waste of money. I tested with a Jensen stepup some years ago, and this confirmed their point. Tubes all the way = best sound, no doubt about it, to my ears. I think the Atlas feeding the Io is a very good match. Some have complained that the Atlas is a bit hard and harsh. Or a bit bright. I don't hear much of that. Rather, the tonal balance is spot on, meaning that the "character" of the cartridge is very hard to identify, since each LP sounds different. I am not saying the Atlas has no faults, but usually, they turn out to be faults of the LP production, or "to the limit" type production (cf Pink Floyd Meddle), or the LP itself (wear), or my turntable setup isn't 100 percent, so whenever I think I have a problem with the cartridge, it disappears on a different type of LP / music /  or with setup tuning. In all, the Atlas/Io combo works great. And the Atlas sounds better on the Hanss T30 player than I ever managed with the VPI HW19 (using the same SME V arm).  

The Atlas isn't harsh! Probably their preamps weren't set up properly!

Maybe. I did a new round of tests. The new Atlas not only sails happily along the trail without any silent woofer pumping (or mistracking), it also reproduces my stress tests cuts beautifully, including Pink Floyd Echoes and tracks from Rickie Lee Jones: The evening on my best day. Passing with flying colors.