Be careful, if the frames are anodized, and you sand and polish them, then your committed to keeping them polished from then on. You may be able to use some very light steel wool and lightly rub away the polish, if done right will do the least amount of damage to what's left of the anodized coating. Not all are anodized but most that I have here are.
You could also clean the aluminum, prime it with self etching primer and zinc chromate and paint it the color of your choice? Flat black, silver, white, etc.
I usually start with the least destructive thing and move up till I get it as you have.
Try some super fine steel wool first, shouldn't hurt anodizing but I don't think it is anodized or it wouldn't be corroding, if that doesn't get it move to 600 sandpaper, make sure you work in a straight line, it will look alot better than random swirls and when you get it off throw a coat of wax on it.
Ya know, it may just be calcium deposits. Have your tried soaking a rag in 50/50 vinegar and water and then laying it on it overnight. If it is calcium it will be gone if not then you're probably right about it being corrosion.
Test it on an inconspicuous place first to make sure it doesn't turn the aluminum black. It its anodized it shouldn't.
Powder coating is a great idea. I plan to do the same with my frames. I had some other pieces already done and the stuff is very durable. I went the polish.... polish again in a month....and polish again until I am tired of it route. Mine are getting coated.
I found my powder coater through work. But they are in the phone book. I found it to be a fairly common trade locally. Very reasonably priced as well, considering what I have to pay my orthopedist to fix my worn out elbows.
Take the frame to a powder coater and have it blasted and coated in the color of your choice.
That's the plan for mine
The price I was quoted was $130, including bead blasting.
Annodizing is just another form of electroplating and puts a hard transparent (or colored) coating on your piece and is not perfect, just convenient long enough to satisfy the first owner and maybe the second one. (much like chrome does.)
Sanding, rubbing and polishing are all contrary to its purpose of protecting.
If you are going to try to get rid of pitting or early stage corrosion under the annodizing, you will most likely cause there to be such a difference in looks, that you will not want the rest of the annodizing to be there when you are done.
Be careful as to who you allow to do the bead blasting and check their work, as bead blasting is also another method of expanding or stressing the surface of your work piece and especially so on softer materials like aluminum, and could leave your item uselessly bent or elongated if not done right.