Knocking noise in dash ( not under the hood) upon starting car

BillBB

Upon starting the car there is a knocking noise coming from the center dash. This is a loud noise that stops after about 15 knocks. But happens upon each start.
Became louder when a new battery was installed.
Also, even after a new battery, the car is slow to start.
Any ideas?

MissieNorris

Did you ever find out what was wring with your Denali? I have one doing the same thing. It goes dead out of no where. When I jump it off it has the knocking sound and then slow starts until it goes out again.

thecardoc3

Without hearing the sound and investigating it, any advice is little more than a guess. That being said, AC system door actuators when they fail can make a clicking sound, and it's not uncommon to hear noise from them when a battery dies. The HVAC control head needs to relearn the door positions if power is lost. Sometimes the aged actuators fail when the system attempts to do the automatic relearn and that results in what could be described as a knocking sound.