Thumping Noise On Cold Start

Hi Everyone,

Subaru Forester Owner Here. I've recently been dealing with a problem that I was hoping to obtain the forums help with.

As of the past few days my vehicle(72,000 miles) has developed a constant thumping/heartbeat noise(for lack of a better way to describe it upon start up from a cold engine. To be more specific the thumping begins about 30/40 seconds after startup and slowly mitigates/goes away once the car is fully warmed up(4/5 minutes-once blue indicator goes away from dashboard). While actually driving no noise is present.

1. I had the serpentine belt/tensioners/pulley replaced about 12,000 miles(7 months ago)
2. I replaced the engine air filter about 10,000 miles(6 months ago)
3. I checked all my fluid levels today(oil level, coolant level etc..) and all are as per specifications at the moment.

The vehicle performs fine but of course the noise concerns me that something is astray and was hoping to get the communities guidance on it. For reference the two videos show what the noise sounds like from inside the car and outside with the hood open respectively. Thanks in advance for any help or leads you can provide!

Engine noise

Noise from Hood Open

 

That sounds like a fan or fan neck/spacer or water pump bearing going out.. but since its only happening for the first few minutes, it doesn't make sense. It does sound like something worn or loose though.

Again, while this wouldn't make any sense, I was wondering if it had something to do with the choke upon initial startup. Maybe running just enough rough during startup/automatic choke, to make something rattle. Then, once the choke shuts off, the rough idle stops & the rattle stops. Its just a theory but I've never run across this before. It could be such light rough idle that you wouldnt notice. Again, it doesnt really make sense but, Its got to be something from initial startup... & the choke was an initial guess.

Hopefully, we can work through this with Q&A and get this resolved. I still think its a rattle... something worn or loose that is actually making the noise. But why only during 3 or 4 minutes on startup.....???

 

Forget most of the above. I failed to listen to the open hood video. Its certainly not a choke/rough idle issue.

Its a rattle... Again, something loose or worn. Its possibly an idler pully but again, the think that has me stumped is, why only 3 or 4 minutes into startup...?????

In some of the noise, I hear what sounds like small metal rubbing against more metal like the idler pully rubbing against the bracket or something. Possibly the bearing in the idler pully was bad... no grease etc. Yes... even a new one. Who installed that stuff recently?

But, I'm still back to square one... why only during 3 or 4 minutes after startup.......??

 

Sounds like an injector, they can produce a rattling noise when cold.

Pull the air cleaner/engine cover off the night before so you can get to them quickly and get a big screw driver so you can put it on each injector and listen to find it.

Carefully of course!

 

Sounds like either fuel injector or exhaust leak. The screwdriver recommendation from Marq is good.
A mechanic's stethoscope would also be helpful, or you can use a 2 foot length of garden hose. Hold one end against each injector and other end to your ear. Also listen around mating point of header to cylinder head.
Looks like your serpentine belt is spinning true, but I'd recommend watching it from the side to see if it wobbles.
It could possibly be valve clatter, but recommend ruling out injectors and exhaust leak first.
As to why only on start up; if exhaust leak then the metal expands and closes leak. Injectors warm up and reduce tolerances. If valve clatter then rods expand when warm and tighten lash.

 

Could be a thermostatic fan clutch if your car has one. Fan is not connected to driven pulley until heat causes clutch to engage the fan and pulley by friction.

 

Thanks for the comments all. I'm not especially mechanic savvy so will have to a bit more reading on parts like the fan clutch and fuel injector but will definitely look into them. As to who installed the pulley/belt/tensioner it was a local mechanic who appeared fairly knowledgeable.

I've done a bit more digging and while I'm still not 100% certain I'm drawing near to concluding that my issue is related to piston slap. I read about it online and have seen a few videos now such as the below which match's up quite well with the sound my vehicle is producing.

I'll keep everyone posted once I'm able to figure it out for good. Thanks for your help thus far!

https://www.youtube.com/watch?v=sgm8...l=hoohoohoblin

 

would probably think it was piston slap also unfortunately.