What you should do

To verify the customer complaint, you need to know the correct (normal) operating behavior of the system and verify that the customer complaint is a valid failure of the system.
The following information will help you verify the complaint:
WHAT the vehicle model/options are
WHAT aftermarket and dealer-installed accessories exist
WHAT related system(s) operate properly
WHEN the problem occurs
WHERE the problem occurs
HOW the problem occurs
HOW LONG the condition has existed (and if the system ever worked correctly)
HOW OFTEN the problem occurs
Whether the severity of the problem has increased, decreased or stayed the same