Relatively new power head (last year). Going across the lake about 20 mph. Engine died with metallic sound. Some time later, I started and limped back to shore. Mechanic ran in tank and said all was well. Said he’d take to lake for 1hr service charge. Ok. He ran about 1 1/2 miles at 20 mph and it died (mechanical noise). This happened three times with good running between dieing. Thoughts? Mechanic?? Is puzzled.