My marbella is emitting an awful screeching noise every now an then.

When I brought the car it would emit the screeching sound quite frequently especially when multiple accessories were in use , such as lights and heater on at the same time.

In an effort to cure the problem I replaced the auxiliary belt which upon inspection had lost multiple teeth and I also replaced the alternator.

This seemed to have cured the problem for the last couple of weeks, but tonight whilst waiting to pull out in traffic it made the noise again!

I'm hoping someone may no the diagnosis
Thanks in advance !

Check the belt tension again, it may have slackened off after initial use. I would also recommend checking the crank pulley is free of any bits of melted/shredded rubber from the old belt when it was slipping, these will be transferred onto the new belt and allow it to slip more easily.

Hiya,You got any idea how tight it should be ? Ill double check it tomorrow in the daylight but I'm sure it was pretty tight after I replaced the alternator

Have a read of this:

https://www.howacarworks.com/electrical-systems/checking-adjusting-and-refitting-drive-belts

Hopefully that will help, around 12-13mm of deflection is usually about right.

I'll have a good look tomorrow, thanks for the pointers!

Forgot to get back to this,thankfully the belt was just loose , screech free