Why is it ringing? | FN SCAR 16

WHERE IS THE RINGING COMING FROM?!?

The FN SCAR 16 is light, fast-handling and quick shooting assault rifle, chambered in 5.56x45mm and features a free-floating, cold hammer-forged MIL-SPEC barrel with chrome-lined bore and chamber.
Fully-ambidextrous operating controls instantly adapt to any shooter and any shooting position. The receiver integrated MIL-STD 1913 optical rail and three accessory rails enable the mounting of scopes or electronic sights, tactical lights and lasers.
The telescoping, side-folding polymer stock is fully adjustable for comb height and length of pull.

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