I own a T2 and a T2 SE. I hunt every day and have 1000s of hours on these machines. I do not have coil covers on them and hunt New England cellar holes almost exclusively. One time my green machine started sounding "blurbly" over targets so I sent it to Felix who "re-shielded" it. That has been the only problem I've noticed. My question is this- should I send my detectors in for tune-ups after so many hours or wait until something acts up? Thank you!!