About 75% of the time, I will get some spurting on extraction. Not much, but enough that it can go onto the floor if I'm not careful. Here's what I've done to try and remedy:

* Removed channeled grinds with Weiss Distribution Technique using a fine dissection needle -- though I'm convinced channeling isn't really an issue anyway (using a Mazzer Super Jolly with doser and never have much clumping or "concentrated" areas)

* Weighing my beans, before grind, to 21g -- sometimes I overdose to about 22g (perhaps I'm underdosing a bit? Because after I tamp, my grinds seem to be very far down in the basket as compared to a double basket)

* Dialed in the grind finer, and triple-tested my tamping vigor to make sure I'm around 30 pounds -- I've gone as fine as I can go, without significantly reducing yield or choking the machine

* I've even dialed down brew pressure (the Quick Mill I'm using has a pressure adjustment knob) to be about 9 bar during extraction (it was 10 bar)

* Beans are usually high quality, but sometimes can be 2 weeks to a month old (I don't burn through coffee as quickly as I should) -- I know that anything over three weeks will be less than optimal, so should I be adjusting my grind fineness as the beans get older? I'm usually using Veltons, Stumptown or right now, Raven's Brew "Three Peckered Goat." The name was too good to pass up.

Just a little frustrated here... I've done quite a bit and still get spurts. The actual extraction usually looks good, with nice crema and tiger striping. It's just the spurting I need to contend with now.

If it tastes good, dont worry about it. I am assuming it is a minor issue. Without a visual it is difficult to say. A spouted portafilter can get a case of the gluggs as air bubbles form from the crema exiting the holes to the spouts. It is all a matter of what the 'spurting' is. As coffee ages, the grind will need tightened up but to the get the most out of the coffee the process is inverse. You actually want to open the grind up then compensate by increasing the dose.

Need to see it...

Have seen poor quality baskets with fine burrs on some holes that can also cause some funny effects...

Poke all the holes with a fine pin from one side and when you rub your finger over the other side you will feel the ones that had a burr of sorts....

Correct those that had a burr and try again.

Are you preinfusing at all? I find that doing so helps normalize things a bit.

You also mentioned that you might be underdosing a bit because of the way the grounds are so deep in the basket. I typically go about 23g in a triple basket. Give it a try, perhaps with a slightly coarser grind so you don't choke the machine.