Hi everyone, I am getting the timing belt, head gasket and all other belts done but I have noticed a whistle / squeal sound at low revs (cant hear it at high revs) and when I switch the motor off I can hear it lower in pitch as it winds down and stops.
Can anyone suggest what it is and if there is something else I should get done at the same time to fix this?
Thanks

 

Noisy belt, vacuum leak, leaking air filter housing?