Startup 'howl'?

[robvas]

Anyone noticed this at all? Once in a while on a cold start (first of the day) when my engine starts I'll hear a weird howling noise. Kind of low pitched 'aarrooo' that lasts about 2 seconds. Doesn't seem to affect anything it's just weird. Not sure if my K&N intake makes it more noticeable or what.

[Newell33]

My truck does this as well. It's hard to describe, but I think you nailed the sound. It's more pronounced after the truck has been setting, or hasn't run for a while.

[tbarn]

Most do it to a degree. Once you hear it, it's hard to miss. My '14 did not have it. My '15 has it but not the worst i've heard. Working in a dealershuip I cold start a lot of these. Some of them I wouldn't buy on a bet. Havig said that, it doesn't seem to hurt anything. Never had a customer complain of the noise.

[ghgmi]

Is there some sort of pump delivering air to pre-warm the cat just after startup?