Is this a common issue and how do I solve it? Bear in mind that I am not a gear geek and have never done any mods on any of my equipment but if I can't solve this issue I'll have to sell the guitar and I don't want to!
It's possible that your tele's pickups could be (very) microphonic? Easy test is if you tap around the pickups with a knuckle (or something non metallic) and you hear a rather audible knocking sound, then you've likely got some microphonic pups - not uncommon in cheaper guitars. Ideally you should only really hear a noise when directly tapping the pickup with a metallic object (screwdriver tip)
Getting the current pups waxed potted should help (or rewound & potted), or a pickup swop - if you like the neck, it's probably worth checking out options. Local options : I've heard good things about Neil Pincus (Rude Rock in Jhb) and Graeme Hayward (Cpt).
I've had some very microphonic pickups - but havn't had those kinda issues with feedback (even when doing a high gain metal thing) - so I'm curious if there is a perhaps another issue. I doubt shielding will help though.