engine noise at startup - goes away after about 30 seconds

2014 2.7L 4-cylinder 5-speed MT 4WD regular cab

This noise doesn't seem to be causing any issues - at least none that I'm aware of. But I'm curious what it is. On a cold start, there will be a high pitched noise for about 30 seconds. I haven't been able to pinpoint where it's coming from yet. After 30 seconds, there's a sound like something spinning down, and then the high pitched noise is gone. I thought maybe it was the fan, but the fan keeps going even after the noise stops. This has been happening ever since I bought the truck about a year ago, so this could be normal, but I'm not sure.

I can hear the high pitched noise in the first half of this video, but I know what to listen for - I'm not sure if you'll be able to. But you can hear the "spin down" noise at the 26 second mark.

https://drive.google.com/file/d/11rxV-SBD-g2PfnzszOowLzlATIZaatG6/view?usp=sharing

Any ideas?

 

That's normal, that is the Secondary Air Injection Pump running.
The system injects fresh air into the exhaust manifold for 30-60 seconds on a cold start to help bring the catyletic converter up to temp.

 

That's great! Thanks for the quick reply! So the high pitched noise doesn't necessarily mean that the pump is starting to fail? Or, if it does fail, will it throw a code?

 

my 3rd gen makes a high pitch ringing noise at startup too sometimes. It literally hurts my ears if i have the windows down. sounds like an ultrasonic cleaner. seems to go away after 30 seconds-one minute. mine's a 4 cylinder too so must be a quirk with the 2tr's.

 

It's normal, the pump is basically a mini vacuum cleaner that blows instead of sucks.
You may want to look into doing the UNI filter mod to prevent failure due to the foam filter degrading.

https://www.youtube.com/watch?v=XO5d4MqZu5I

 

Thanks very much. I'll check it out.

 

Think there is a Mod for that

 

Do the uni filter mod now.....it's so simple, it's cheap, and saves you so much money in the
Long run.

 

that filter mod is one of the first things i did to my truck. super easy. good opportunity to clean your MAF at the same time also.