I recently bought a 1998 astro boat from vics sport center in ohio with a 1998 175hp efi,when I got it home and took it to the lake I noticed a horrible knock in the motor,I'm gonna try to post a video or 2 ,can you mercury experts give me advice Wether I should be worried or is this a normal sound like their mechanic says it is ,I really need help because I don't want to ruin the motor. Serial# og665721,175hp efi 1998 max rpms 5600,I haven't had it over 4k,and there is no water temp or pressure gauge on. .ok how do I post a video on here?