Trojan Boat Forum

could be the pump has sucked up a bit of flotsam, and needs to be cleared (may need to disassemble). On the other hand, vibration may be caused by a loose mount to the bulkhead. There may be rubber grommets in the mounting holes to deaden sound of pump operation, and one or more of those grommets may be worn away.

Belt driven diaphragm pumps vibrate a lot. Check (if it exists)your inline filter.