the screeching could be that the cam bearing in the seawater pump that actuates the fuel pump is dry of gear lube. pull the overfill screw on the pump and see if it has gear lube in it.
try adjusting the switch! its on top of the elongated cylinder. if that doesn't do it you need a new switch. Happened to me in the late summer. DOMETIC 385318032 VACUUM TANK SWITCH KIT NEW (163)Opens in a new window or tab
double check your model before ordering.
if you have Hurth Trans. there is a Bulletin release about that. it talked about the gear noise you would get at low idle speed, the trans gears would not mesh and the bulletin said to use motor oil rather than ATF.
SERVICE ADVISORY Date: 11/21/01 Advisory #SV2001-2 SUBJECT: Gear Rattle Hurth...