Linas, A fault cannot be identified as falling within Warranty cover until an appropriate investigation has been completed.
If upon completion a fault does exist and the remedy falls within the terms of the Warranty cover, then yes the entire cost can be charged to the Warranty.
If however upon completion of the investigation, a fault does not exist, then the costs of the investigation fall to be borne by the customer.
One does not check under Warranty, one fixes under Warranty.