This link, posted by Secondtry (Thank you!) earlier today, clarifies very fully the issue re magnesium.
It quotes arrythmias as a 'possible cardiovascular manifestation of magnesium deficiency' and also lists 'tinnitus' as a 'potential clinical sign of magnesium deficiency'. How many people here would be much healthier if they and their doctors took this to heart (provided they don't have kidney disease)?
('Potential' and 'possible' should be read as indicating that no researcher will say 'this is the only cause' in relation to anything, as there is always more to learn!)