2 Strange Sounds in CC - Engine & Rear Suspension

[Elmura]

G'day all good folk,
My V6 4Motion MY12 Passat CC has 2 odd sounds, both intermittent.

One is a type of faint engine squeal that increases in pitch with RPM. It can only be heard from the cabin, can not be heard from the engine bay itself with someone revving it (but the occupants can hear it). Definitely engine related as it's heard as revs rise whether driving or in Park; whether it's exhaust leak (but I figure that should make a loud obvious sound); vacuum leak; could be chain drive but kms are very low (37000km). Ideas?

Second is a rear suspension squeak. Again, 37000km. Springs are lowered Eibach which have been on car for over 20,000km, the rest of suspension is stock. I've tried to get someone to bounce the car while I narrow in on the spot but no luck yet as it's very intermittent.

Ideas?

[Elmura]

Found the source of the noises after weeks of investigation -but need a fix.
Engine squeal noise is coming through the air vents only. Only makes noise when thermostat is at low or cool temperatures WITH A/C off. Turn heat up to max & noise goes away with fan at lowest setting. Not fan noise as the pitch increased with RPM. So, I'm figuring it's a leaky thermostat valve?

Rear noise turns out not to be suspension but -get this- a creaking left side fuel tank. I tightened the tank straps but noise still occurs ONLY if you push up in the centre of the tank where there is a rectangular depression. If you push up anywhere else, no noise. So I'm figuring a loose fuel pump?

Any knowledge about a fix for either of these?

Revhead by nature