What is the policy of the warranty on non-original Lenovo drives? Ie. my X220 came with a Seagate 250gb hdd, but if I happen to install a different hdd or ssd but one that's a Lenovo part will my X220's warranty cover it since it's a Lenovo part? I'm asking since the manufacturer doesn't warranty the part since it's a Lenovo OEM unit.
In general, the warranty for the system covers the components that were in the system at the time it was manufactured, as per the original shipping configuration list.
If you buy a Lenovo HDD or SDD that is different to the drive in the original configuration and put it in the system, it would be covered by whatever warranty applied to that component, rather than the system warranty.