I would play with feeds & speeds because your not cutting properly.? Your cutting and shoving.!! Look at the vid about 1:28 and you'll see the material being curled not cut.!! . . . Basicly it's being shoved out the way not cut.
Also the chatter and resonance is quite high even thou your (rightly) conventional milling, this dull tools quickly and puts extra stress's on the machine and spindle which will prematurely wear out bearings etc.!!

I can tell the cutting set-up is wrong from the sound, when it comes to cutting Aluminium then it's slightly different from other materials regards DOC etc so it's important to find the machines sweet spot regards spindle RPM and depth of cut (DOC). This you can tell from the noise and harmonics of the machine.

This is will be different for every machine or should say most machines that are not identical.? For instance no point me telling you my set-up for cutting aluminium because my machine is completely different. It also changes with cutter size and length, even the tools material makes a big difference.

Really You need to find the machines "Sweet spot" for the machines life and your pockets sake, not to mention finished quality.!! . . At the rate I'm hearing you'll wear this machine out very quickly.
It takes some trial and error but worth it if your going to cut lots of aluminium and believe it or not can result in you being able to cut deeper with less chatter by finding the natural harmonic balance of cutting tool and machine.? . . Trial and error is the only way but it can be done quickly if done in a methodical manner.

Check this out and while it's aimed at commercial machines the principles the same. It also gives a procedure to follow that will help find the sweet spot.
It works and the difference is noticeable in both sound has well has visual not to mention performance.

http://www.mmsonline.com/articles/maximum-aluminum