knocking sound in cold weather

[a77ms25]

hi all

i have a new problem with my corolla 2009, it produce's a knocking sound during starting at cold weather since three days, today i chanched the oil and the sound is less but i still can hear it do u think i have a serious problem with my engin or its normal and it will be disappears in the future.

[keyboardracer]

its like a faint trumping noise?
Is your car park outside at ambient lower than 10F? or -15C

is it only occur when you idle and rev it to 2000 rpm?

It could be your accessory belt get stiff under cold temperature.

[a77ms25]

i do park outside and the temp. around +3C

the noise appears during first start at early morning only and it disappear after three minutes
no the noise does not appeare at 2000 rpm

[lee0]

nice gen 2009