So for about a year I get this weird grinding noise sporadically coming from behind my radiator fans. It's like a grinding/clicking noise. For a while I've just thought it was a bearing issue with one of the fans, they both spin fine so I thought nothing of it. Car doesn't overheat, never had a problem with that, stays around normal temperature. It hadn't happened in about 4 months until today when I heard it again. I finally decided to check on it and maybe buy a new fan to replace it. I had my girlfriend rev the engine a bit (seems to happen most when the engine has come up to temp and been run a little hard/for a long time and when the weather is warm) and sure enough, it sounded like it was coming from the passenger side fan, but then that fan shut off on the noise continued. It seems like it's coming from inside the engine right behind the fans, but it doesn't seem to be muffled or anything so I find it hard to believe it's coming from inside the block.

I'm at a complete loss here, not sure what it could be at this point, and it would be pointless to take it to a mechanic unless I happen to pass one at the exact moment the sound starts. It's hard to duplicate it, hard to get the car to make the sound, and on top of it all the sound doesn't always last very long

 

could be worn main bearings or rod bearings

 

Wouldn't that be a pretty constant sound? This sound happens randomly and has no pattern to the clicking/grinding.

 

Oh I read wrong. Check your exhaust manifold bolts or heat shield. Check for anything that expands and contracts with heat that may cause your sound

 

My heat shield is gone, manifold bolts are tight but I did notice that there's a small crack in one of the pipes. It's not deep enough to be a problem yet but I guess this is just an excuse to get a header
I'll see if I can pinpoint the sound better today while I'm driving. It's another hot day.

 

It's a small crack, think I should replace it? Here's a picture. It goes all the way around.

 

That could be the source of your noise. It's not on a tube so it's not leaking exhaust into the hood and scorching everything like mine is.

 

Yeah I just dropped it off at my mechanic an hour ago and he's going to check out my rotors and see if he can find the sound. I'm going to replace it anyway soon with a header, so we'll see how things go.

 

Update: My mechanic traced the sound to my A/C. Happens when the pump kicks on. It's just starting to go because of old age, not really worth it for me to replace since I live in a cold climate. Maybe I'll just do an A/C delete sometime in the future.

 

haha I did PS and FULL a/c delete and I live in FL....hahaha summers are hotttttttt but the faster you drive you get mother natures a/c bwahahaha