Hi i have a octavia mk2 vrs with no mods.I've started to notice that at times the door speakers are distorting and vibrating.

It appears to be just the small speakers which are located in the area of the handle.

I take it this means they are on the way out. How easy will these be to replace, and what would be the best speaker to install.

Thanks

It means its a good time to upgrade. The Hertz Deici range are good off headunit power. Alternatively just get an oem replacement of you're happy with the factory sound. If the door cards are vibrating stick some deadening on them too whilst you have the door cards off.