See the advice re setting up the drive cable tension properly elsewhere on this site. You won't typically find better advice about this anywhere else.
The fins hitting the underside of the hull at full leg extension can cause a noise. The solutions are:
1. Check that the fins are aligned correctly - with the pedals lined up with each other and both on the same leg-length adjustment both fins should point more or less vertically downwards when viewed from the front/back of the drive. If they do not then it is possible that one chain is out of alignment with the other (in other words one chain is one tooth "out" compared to the other). If you are a tooth "out" you will need to slacken off the offending cable and "unskip" that tooth.
2. Move the pedals to a shorter leg length - so that the fins don't hit the hull when you have your leg fully extended.
3. Moderate your pedalling action so that you don't push your foot as far out thus avoiding the fins hitting the hull.
N.B. When your leg is at full extension at the end of a pedal stroke, your knee should remain slightly bent: you should not have your knee fully flattening out or overextending at the bottom of the stroke.
My suggestion would be to take it easy in the early days til you are "match fit". Even if you are a super-fit super-hero like I was
the pedalling action is probably still somewhat different from what you have been used to (e.g. cycling/running/walking/stepping) and you may find that if you overdo it you get tweaks and twinges in your legs that you would prefer to do without. This is most likely with the turbo fins though once you have built up your pedalling fitness you may find that using the standard fins feels like "pedalling in air". The Turbo fins do put more stress on the legs and drive compared to the standard fins, especially if you push hard.