Odd left stick issues on wireless controller.

Sorry you're having issues with your controller. The issues that you're describing does sound like faulty hardware unfortunately. As such per the accessory warranty if you've had it over 90 days, the only option would be to purchase a new controller. Totally understand how frustrating that can be. If you've had it less than 90 days please go to this link and request a repair on the controller. Below is the link to the Xbox Warranty. 

Xbox Warranty. 

To answer your other questions. 

Does anyone know what could cause this? Usually hardware issue when drifting happens. 

Is there an easy fix for it that I can do myself (easy as in not having to solder anything)? There is not a fix. If your controllers are up to date repair is the only option. DIY fixes are against the forums TOU. 

And what is the warranty on a wireless controller? (I've had this controller for less than a year.): 90 days. 

I have the exact same problem and I think my controller is just over 90 days old. I am very careful with my equipment and it's disappointing to see official microsoft hardware fail so quickly especially considering how expensive it is. The last time I had microsoft replace a controller, (yes this has happened before) they made me pay for shipping which was around $20 because I had to buy a box and packaging materials as well. And on top of that, they will not ship your new controller until they receive your faulty one. So you're looking at well over a month and possibly around 2 months to get a new controller. I recommend buying a new one. Hopefully microsoft will fix these faults in future models. Meanwhile, the best we can do is spread awareness of these faults.

Since it was past warranty, I decided to open it up myself. I cleaned it and surprisingly it's working again. No problems at all...for now.

As for the solution of "buy a new one"...I feel that isn't the right choice. Why reward Microsoft with more of my money when the first controller I purchased from them would start to have issues in less than year's time. That's inexcusable and not only that...how do I know the same thing wouldn't just happen again with the next controller.

What needs to happen is MS needs to address this problem that I have noticed a lot of other people have. Either extend the warranty or fix the design of their product.

Hi Doh  Ray Egon,

Thanks for the input. That said posting DIY fixes are against the forums terms of use.