May be Black sand, Mineralization greatly effects stabitily.
Here on West Coast, River black sand is terrible which creates masking. VLF struggle, but models with prospecting mode and SAT this greatly helps with stabitily. Try prospecting mode, increase SAT start around 5 and adjust from there. Don't worry about loosing depth, you'll gain some depth back with smoother stabitily bumping up SAT. Then, reduce SAT if it's too stable look for a happy medium and adjust sensitivity as well you can operate with high sens bumping up SAT.
Proper GB, use SAT in prospecting mode this will eliminate the noise you're hearing.
Plus, hunt with zero discrimination. Medium to smaller gold jewelry will ID as iron because black sand tends to drop ID into iron range. Even high conductive coins will ID in iron range, depending how bad mineralization is.
I use my MX Sport in water, with the 7" Detech or stock 10". Prospecting mode is the secret to VLF water hunting, And because the MX Sport has a SAT feature that separates it from other waterproof detectors.
Good luck,
Paul