2008 impreza 2.5 ,180,000 KM engine sound louder on cold start up quits down after few minutes .It is summer time now it did not make this louder noise in winter.
I’d think there is a small leak in the exhaust system. Possibly the manifolds at the head. Stuff a large potato in the exhaust pipes when the engine is cold, start it up and listen and feel for the sound of rushing gas. When you find it, that is the leak. Rev the engine a small bit and the potatoes should pop out.
Do not eat the potato!!!
I thought it might be something
along that line , i am an electrican not a car guy,thank you.