has anybody got any idea why my MK2 has suddenly started to get lots of noise this happens about 5 minutes after turning it on and gradually gets worse, if i turn it off & on again the same thing happens over & over. i have tried changing coils but the only thing that changes is that the problem gets worse the bigger the coil that i use, i have tried turning the sensitivity down but that dont work either, ihave also tried various batteries, the noise dissapears when the coil is disconnected, please help as i love this machine and have had lots of great finds over the last 2 years