"İs it the rudder bearings or draglink bearing or some other part.?"
Hi lucco,
Some time back I was on a friends B37 when a strange sound similar to that which you have described was heard. At the time we had the engine running, and on investigation within the compartment aft of the two stern cabins where the steering system is located, we found that the engine exhaust hose securing in one place had broken. This allowed the hose to move around in time with the pulses of water that were being ejected overboard from the exhaust system, and resulted in the hose knocking repeatedly against the port cabin aft bulkhead. The securing strap which consisted of a short length of perforated stainless steel, had broken, and this had allowed the hose to move around. We were concerned that Without immediate attention the hose might detach itself from the exhaust overboard outlet, which in turn might have filled the boat with smoke, water, and more importantly carbon monoxide gas which is a killer, so temporarily we fitted a rope lashing until we got into port where a more permanent securing was made.
Subsequent investigation on my own B36 revealed two broken securing strips for the exhaust hose which had remained in place without making any noise, so those securings are worth checking anyway.