We have taken our car into Holden to be repaired.

We have taken our car into Holden to be repaired as when we start it on a cold morning it makes a whirring/clicking noise for approx. 3 seconds. We have picked it up from Holden twice and this is the third time we've taken it back and the mechanics are saying there was sludge in the motor and even this time apparently there was still sludge in the motor even though this is the third time they have had the car in about 2 weeks. Does this sound right or not really? Any help greatly appreciated! Thank you