Which is Quieter -- Stock Gen 2 Marauder (.22) or a Stock Gen 2 Fortitude (.22)?

I believe they are both using the same baffle system, the Marauder is capable of more power. A 177 tuned about 15 ft. pounds is quieter than a hi twenties .22 and that is less than a 40 ft.pound .25. The older Disco shooting at 20 plus ft. pounds is loudest with a straight barrel.

Not specifically an answer to your question but ... Gen II Stormrider in .22 is about the quietest PCP I've ever not heard. You can hear the valve spring pinging and the slap on the target and that's about it. It is about 25 FPE. My BSA Lonestar with the custom moderator was pretty quiet but not as quiet as the Stormrider.

I have a Marauder tuned to about 24fpe. All I can say is that it is about 88 db inches from the muzzle. Don't have any experience with the Fortitude so can't say. AEAC did a review on the original Fortitude that Crosman withdrew and fixed a few things on, and its at about 6:35 here:

https://www.youtube.com/watch?v=eUuPs2RL12o

It was under 70, but the power was set way low. 18fpe, so the gun will be quieter just from the reduced power.

Looks like the guns run about the same noise level, but haven't actually tested both side by side with equal power settings.

I have had both...still have the fortitude. To my ears, the fortitude was quieter but it was also shooting with a little less energy. I can say that I really like my Fortitude with the ugraded Baker trigger. Fun, accurate and light weight.

I have both. Well sort of, the Gen 2 Fortitude is 177 cal. The Fortitude only has 3 baffles to the Mrod 7, same shroud. The difference is in the barrel length, mrod 20" to Fort 23.25". At the same power level, the Mrod is noticeably quieter. The Fortitude is regulated, which eliminates ping. The Mrod will have some ping.

FWIW: I built a 40fpe 25 cal from my Gen 1 177 Fortitude, which uses the Mrod barrel and 7 baffles, and it is still significantly quietter than the 177 was. 

Both are mouse fart quiet.

The two guns are significantly different, in size, weight, and power capability. The primary decision would be better focused on something that can not be easily changed. Whichever you choose, and it is not quiet enough for your needs, lots of choices out there to fix that.