Recently a sqeal has developed in my 124 300D 2.5 turbo. It sounds like it is comming from inside the dash. These are the conditions:

Climate control on low - intermittant squeal
CC on high - No squeal
A/C on low - intermittent squeal
A/C on high - No squeal
CC off no squeal

It sounds like a loose belt. Is there a belt driving the motor?

How to fix?