A few months ago, while playing Oblivion, I discovered that my 360 controller had gotten a Squeaky right trigger from using it too much: it would make a weird squeak every time I used it.

I have this, but my volume is up high when I play so I don't really notice it...

I have the same problem with my PS3 controller, though my 360's is fine.

Try a light spray of white lithium grease, that'll take care of the problem. 

My 360 controller does it too, but it's quiet and doesn't really bother me.

Yep. Bugs the hell outta me sometimes.

Yeah, I've had that. Sometimes my back button has been stuck too (not sticky/slow to press down but just stuck against the plastic shell).

Oh, it's my trigger that's squeaking--I thought it was my old fingers creaking. 

The right trigger on my controller has always been squeaky, but I got used to it and stopped noticing. That is, until you mentioned yours being squeaky just now.. Now I need to learn to ignore it all over again. I hate you...

I think I had this problem, where it should squeak every now and then. But I barely even notice it.

nope. never had this problem. :)

I have a controller with this problem.  I don't use it though.

i have that and its a good thing for me :) cuz in COD4 i use the G3 and it makes me shoot faster

Yep, my Ps2 does it with it's analog stick. It annoys me because it also hinders movent of the analog stick, so it makes gameplay hard.

White lithium grease as has been said or a tooth pick and some olive oil get the pivot bar inside with it a few times.

I would reccomend taking the controller apart but...alas it has weird screws.